diff --git a/src/cmd/changelog-cli/main.go b/src/cmd/changelog-cli/main.go
index f2e9f7c..7b6a622 100755
--- a/src/cmd/changelog-cli/main.go
+++ b/src/cmd/changelog-cli/main.go
@@ -78,7 +78,7 @@
 	if err != nil {
 		return fmt.Errorf("generateChangelog: failed to create http client: \n%v", err)
 	}
-	sourceToTargetChanges, targetToSourceChanges, err := changelog.Changelog(httpClient, source, target, instance, manifestRepo, -1)
+	sourceToTargetChanges, targetToSourceChanges, err := changelog.Changelog(httpClient, source, target, instance, manifestRepo, "", -1)
 	if err != nil {
 		return fmt.Errorf("generateChangelog: error retrieving changelog between builds %s and %s on GoB instance: %s with manifest repository: %s\n%v",
 			source, target, instance, manifestRepo, err)
diff --git a/src/cmd/changelog-webapp/app.yaml b/src/cmd/changelog-webapp/app.yaml
index 38ba74c..c365fc5 100644
--- a/src/cmd/changelog-webapp/app.yaml
+++ b/src/cmd/changelog-webapp/app.yaml
@@ -23,3 +23,4 @@
   COS_INTERNAL_FALLBACK_GERRIT_INSTANCE_NAME: "cos-internal-fallback-gerrit-instance"
   COS_INTERNAL_GOB_INSTANCE_NAME: "cos-internal-gob-instance"
   COS_INTERNAL_MANIFEST_REPO_NAME: "cos-internal-manifest-repo"
+  CROSLAND_NAME: "crosland-url"
diff --git a/src/cmd/changelog-webapp/controllers/pageHandlers.go b/src/cmd/changelog-webapp/controllers/pageHandlers.go
index 20bf4e5..31a558e 100644
--- a/src/cmd/changelog-webapp/controllers/pageHandlers.go
+++ b/src/cmd/changelog-webapp/controllers/pageHandlers.go
@@ -40,6 +40,7 @@
 	internalFallbackGerritInstance string
 	internalGoBInstance            string
 	internalManifestRepo           string
+	croslandURL                    string
 	externalGerritInstance         string
 	externalFallbackGerritInstance string
 	externalGoBInstance            string
@@ -78,6 +79,10 @@
 	if err != nil {
 		log.Fatalf("Failed to retrieve secret for COS_INTERNAL_MANIFEST_REPO_NAME with key name %s\n%v", os.Getenv("COS_INTERNAL_MANIFEST_REPO_NAME"), err)
 	}
+	croslandURL, err = getSecret(client, os.Getenv("CROSLAND_NAME"))
+	if err != nil {
+		log.Fatalf("Failed to retrieve secret for CROSLAND_NAME with key name %s\n%v", os.Getenv("CROSLAND_NAME"), err)
+	}
 	externalGerritInstance = os.Getenv("COS_EXTERNAL_GERRIT_INSTANCE")
 	externalFallbackGerritInstance = os.Getenv("COS_EXTERNAL_FALLBACK_GERRIT_INSTANCE")
 	externalGoBInstance = os.Getenv("COS_EXTERNAL_GOB_INSTANCE")
@@ -337,7 +342,7 @@
 		http.Redirect(w, r, loginURL, http.StatusTemporaryRedirect)
 		return
 	}
-	added, removed, utilErr := changelog.Changelog(httpClient, source, target, instance, manifestRepo, querySize)
+	added, removed, utilErr := changelog.Changelog(httpClient, source, target, instance, manifestRepo, croslandURL, querySize)
 	if utilErr != nil {
 		log.Errorf("error retrieving changelog between builds %s and %s on GoB instance: %s with manifest repository: %s\n%v\n",
 			source, target, externalGoBInstance, externalManifestRepo, utilErr)
diff --git a/src/pkg/changelog/changelog.go b/src/pkg/changelog/changelog.go
index 866b929..265e399 100644
--- a/src/pkg/changelog/changelog.go
+++ b/src/pkg/changelog/changelog.go
@@ -105,7 +105,7 @@
 	}
 	buildNum := strings.Replace(build[2], "-", ".", 3)
 	log.Debugf("resolveImageName: image name %s was resolved to build number %s", imageName, buildNum)
-	return strings.Replace(build[2], "-", ".", 3)
+	return buildNum
 }
 
 // Creates a unique identifier for a repo + branch pairing.
@@ -320,7 +320,7 @@
 //
 // The second changelog contains all commits that are present in the source build
 // but not present in the target build
-func Changelog(httpClient *http.Client, source string, target string, host string, repo string, querySize int) (map[string]*RepoLog, map[string]*RepoLog, utils.ChangelogError) {
+func Changelog(httpClient *http.Client, source, target, host, repo, croslandURL string, querySize int) (map[string]*RepoLog, map[string]*RepoLog, utils.ChangelogError) {
 	if httpClient == nil {
 		log.Error("httpClient is nil")
 		return nil, nil, utils.InternalServerError
@@ -335,13 +335,14 @@
 	if err != nil {
 		return nil, nil, err
 	}
-	sourceRepos, err := mappedManifest(manifestClient, repo, sourceBuildNum)
-	if err != nil {
-		return nil, nil, err
-	}
-	targetRepos, err := mappedManifest(manifestClient, repo, targetBuildNum)
-	if err != nil {
-		return nil, nil, err
+	sourceRepos, sourceErr := mappedManifest(manifestClient, repo, sourceBuildNum)
+	targetRepos, targetErr := mappedManifest(manifestClient, repo, targetBuildNum)
+	if sourceErr != nil && sourceErr.HTTPCode() == "404" && targetErr != nil && targetErr.HTTPCode() == "404" {
+		return nil, nil, utils.BothBuildsNotFound(croslandURL, source, target)
+	} else if sourceErr != nil {
+		return nil, nil, sourceErr
+	} else if targetErr != nil {
+		return nil, nil, targetErr
 	}
 
 	clients[host] = manifestClient
diff --git a/src/pkg/changelog/changelog_test.go b/src/pkg/changelog/changelog_test.go
index e309b8e..8a17a8a 100644
--- a/src/pkg/changelog/changelog_test.go
+++ b/src/pkg/changelog/changelog_test.go
@@ -64,7 +64,7 @@
 	httpClient, _ := getHTTPClient()
 
 	// Test invalid source
-	additions, removals, err := Changelog(httpClient, "15", "15043.0.0", cosInstance, defaultManifestRepo, -1)
+	additions, removals, err := Changelog(httpClient, "15", "15043.0.0", cosInstance, defaultManifestRepo, "", -1)
 	if additions != nil {
 		t.Errorf("changelog failed, expected nil additions, got %v", additions)
 	} else if removals != nil {
@@ -76,7 +76,7 @@
 	}
 
 	// Test invalid target
-	additions, removals, err = Changelog(httpClient, "15043.0.0", "abx", cosInstance, defaultManifestRepo, -1)
+	additions, removals, err = Changelog(httpClient, "15043.0.0", "abx", cosInstance, defaultManifestRepo, "", -1)
 	if additions != nil {
 		t.Errorf("changelog failed, expected nil additions, got %v", additions)
 	} else if removals != nil {
@@ -88,7 +88,7 @@
 	}
 
 	// Test invalid instance
-	additions, removals, err = Changelog(httpClient, "15036.0.0", "15041.0.0", "com", defaultManifestRepo, -1)
+	additions, removals, err = Changelog(httpClient, "15036.0.0", "15041.0.0", "com", defaultManifestRepo, "", -1)
 	if additions != nil {
 		t.Errorf("changelog failed, expected nil additions, got %v", additions)
 	} else if removals != nil {
@@ -100,7 +100,7 @@
 	}
 
 	// Test invalid manifest repo
-	additions, removals, err = Changelog(httpClient, "15036.0.0", "15041.0.0", cosInstance, "cos/not-a-repo", -1)
+	additions, removals, err = Changelog(httpClient, "15036.0.0", "15041.0.0", cosInstance, "cos/not-a-repo", "", -1)
 	if additions != nil {
 		t.Errorf("changelog failed, expected nil additions, got %v", additions)
 	} else if removals != nil {
@@ -112,7 +112,7 @@
 	}
 
 	// Test build number higher than latest release
-	additions, removals, err = Changelog(httpClient, "15036.0.0", "99999.0.0", cosInstance, defaultManifestRepo, -1)
+	additions, removals, err = Changelog(httpClient, "15036.0.0", "99999.0.0", cosInstance, defaultManifestRepo, "", -1)
 	if additions != nil {
 		t.Errorf("changelog failed, expected nil additions, got %v", additions)
 	} else if removals != nil {
@@ -124,7 +124,7 @@
 	}
 
 	// Test manifest with remote urls specified and no default URL
-	additions, removals, err = Changelog(httpClient, "1.0.0", "2.0.0", cosInstance, defaultManifestRepo, -1)
+	additions, removals, err = Changelog(httpClient, "1.0.0", "2.0.0", cosInstance, defaultManifestRepo, "", -1)
 	if additions == nil {
 		t.Errorf("changelog failed, expected additions, got nil")
 	} else if removals == nil {
@@ -248,7 +248,7 @@
 		"9bc12bb411f357188d008864f80dfba43210b9d8",
 		"bf0dd3757826b9bc9d7082f5f749ff7615d4bcb3",
 	}
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, -1)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", -1)
 	if err != nil {
 		t.Errorf("changelog failed, expected no error, got %v", err)
 	} else if len(removals) != 0 {
@@ -292,7 +292,7 @@
 		"src/platform2",
 		"src/third_party/chromiumos-overlay",
 	}
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, -1)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", -1)
 	if err != nil {
 		t.Errorf("changelog failed, expected no error, got %v", err)
 	}
@@ -306,7 +306,7 @@
 	source = "15030.0.0"
 	target = "15050.0.0"
 	querySize := 50
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, querySize)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", querySize)
 	if err != nil {
 		t.Errorf("changelog failed, expected no error, got %v", err)
 	} else if additions == nil {
@@ -332,7 +332,7 @@
 	// Test changelog handles manifest with non-matching repositories
 	source = "12871.1177.0"
 	target = "12871.1179.0"
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, querySize)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", querySize)
 	if err != nil {
 		t.Errorf("changelog failed, expected no error, got %v", err)
 	} else if len(removals) != 0 {
@@ -357,7 +357,7 @@
 	// Test with different release branches
 	source = "13310.1035.0"
 	target = "15000.0.0"
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, querySize)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", querySize)
 	if err != nil {
 		t.Errorf("Changelog failed, expected no error, got %v", err)
 	} else if len(additions) == 0 {
@@ -369,7 +369,7 @@
 	// Test empty repository
 	source = "0.0.0"
 	target = "2.0.0"
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, querySize)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", querySize)
 	if additions != nil {
 		t.Errorf("changelog failed, expected nil additions, got %v", additions)
 	} else if removals != nil {
@@ -383,7 +383,7 @@
 	// Test image name
 	source = "cos-rc-85-13310-1034-0"
 	target = "cos-rc-85-13310-1030-0"
-	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, querySize)
+	additions, removals, err = Changelog(httpClient, source, target, cosInstance, defaultManifestRepo, "", querySize)
 	if err != nil {
 		t.Errorf("Changelog failed, expected no error, got %v", err)
 	} else if len(additions) != 0 {
diff --git a/src/pkg/utils/changelogerror.go b/src/pkg/utils/changelogerror.go
index f5b415f..f59a206 100644
--- a/src/pkg/utils/changelogerror.go
+++ b/src/pkg/utils/changelogerror.go
@@ -23,6 +23,7 @@
 	"errors"
 	"fmt"
 	"regexp"
+	"strings"
 
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
@@ -119,13 +120,63 @@
 	return innerErr
 }
 
+func croslandLink(croslandURL, source, target string) string {
+	return fmt.Sprintf("%s/log/%s..%s", croslandURL, source, target)
+}
+
+// BothBuildsNotFound indicates that neither build was not found
+func BothBuildsNotFound(croslandURL, source, target string) *UtilChangelogError {
+	return &UtilChangelogError{
+		httpCode: "404",
+		header:   "Build Not Found",
+		err: strings.Join([]string{
+			"The builds associated with input",
+			source,
+			"and",
+			target,
+			"cannot be found. It may be possible that the inputs are either invalid or both belong",
+			"to pre-Cusky builds. If both of the inputs belong to pre-Cusky builds, note that this tool only supports changelogs",
+			"between Cusky builds. Otherwise, please input valid build numbers (example: 13310.1035.0) or valid image names",
+			"(example: cos-rc-85-13310-1034-0).",
+		}, " "),
+		htmlErr: fmt.Sprintf("%s %s and %s %s<br><br>%s %s <a href=%s target=\"_blank\">%s</a>. %s %s",
+			"The builds associated with input",
+			source,
+			target,
+			"could not be found.",
+			"It may be possible that the inputs are either invalid or both belong to pre-Cusky builds.",
+			"If both of the inputs belong to pre-Cusky builds, please check",
+			croslandLink(croslandURL, source, target),
+			croslandLink(croslandURL, source, target),
+			"Otherwise, please input valid build numbers",
+			"(example: 13310.1035.0) or valid image names (example: cos-rc-85-13310-1034-0).",
+		),
+	}
+}
+
 // BuildNotFound returns a ChangelogError object for changelog indicating
 // the desired build could not be found
 func BuildNotFound(buildNumber string) *UtilChangelogError {
 	return &UtilChangelogError{
 		httpCode: "404",
 		header:   "Build Not Found",
-		err:      fmt.Sprintf("The build associated with input %s cannot be found. Please input a valid build number (example: 13310.1035.0) or a valid image name (example: cos-rc-85-13310-1034-0).", buildNumber),
+		err: strings.Join([]string{
+			"The build associated with input",
+			buildNumber,
+			"cannot be found. It may be possible that the input is either invalid or belongs to a",
+			"pre-Cusky build. If you entered a pre-Cusky build number or image name, note that changelog between",
+			"pre-Cusky and Cusky builds are not supported. Otherwise, please input a valid build number",
+			"(example: 13310.1035.0) or a valid image name (example: cos-rc-85-13310-1034-0).",
+		}, " "),
+		htmlErr: fmt.Sprintf("%s %s %s<br><br>%s %s %s %s",
+			"The build associated with input",
+			buildNumber,
+			"cannot be found.",
+			"It may be possible that either the input is either invalid or belongs to a",
+			"pre-Cusky build. If you entered a pre-Cusky build number or image name, note that changelog between",
+			"pre-Cusky and Cusky builds are not supported. Otherwise, please input a valid build number",
+			"(example: 13310.1035.0) or a valid image name (example: cos-rc-85-13310-1034-0).",
+		),
 	}
 }
 
diff --git a/src/pkg/utils/changelogerror_test.go b/src/pkg/utils/changelogerror_test.go
index e636449..f24ea1a 100644
--- a/src/pkg/utils/changelogerror_test.go
+++ b/src/pkg/utils/changelogerror_test.go
@@ -17,6 +17,7 @@
 import (
 	"errors"
 	"fmt"
+	"strings"
 	"testing"
 
 	"google.golang.org/grpc/codes"
@@ -28,7 +29,7 @@
 )
 
 func testCLLink(clID, instanceURL string) string {
-	return fmt.Sprintf("<a href=\"%s/q/%s\" target=\"_blank\">CL %s</a>", instanceURL, clID, clID)
+	return fmt.Sprintf("<a href=\"%s/c/%s\" target=\"_blank\">CL %s</a>", instanceURL, clID, clID)
 }
 
 func TestGerritErrCode(t *testing.T) {
@@ -87,11 +88,69 @@
 	}
 }
 
+func TestBothBuildsNotFound(t *testing.T) {
+	source := "1a"
+	target := "ddddddd"
+	croslandURL := "https://www.google.com"
+	expectedCode := "404"
+	expectedErrHeader := "Build Not Found"
+	expectedErrStr := strings.Join([]string{
+		"The builds associated with input",
+		source,
+		"and",
+		target,
+		"cannot be found. It may be possible that the inputs are either invalid or both belong",
+		"to pre-Cusky builds. If both of the inputs belong to pre-Cusky builds, note that this tool only supports changelogs",
+		"between Cusky builds. Otherwise, please input valid build numbers (example: 13310.1035.0) or valid image names",
+		"(example: cos-rc-85-13310-1034-0).",
+	}, " ")
+	expectedHTMLErrStr := fmt.Sprintf("%s %s and %s %s<br><br>%s %s <a href=%s target=\"_blank\">%s</a>. %s %s",
+		"The builds associated with input",
+		source,
+		target,
+		"could not be found.",
+		"It may be possible that the inputs are either invalid or both belong to pre-Cusky builds.",
+		"If both of the inputs belong to pre-Cusky builds, please check",
+		croslandLink(croslandURL, source, target),
+		croslandLink(croslandURL, source, target),
+		"Otherwise, please input valid build numbers",
+		"(example: 13310.1035.0) or valid image names (example: cos-rc-85-13310-1034-0).",
+	)
+	err := BothBuildsNotFound(croslandURL, source, target)
+	if err.HTTPCode() != expectedCode {
+		t.Errorf("expected HTTP code %s, got %s", expectedCode, err.HTTPCode())
+	} else if err.Header() != expectedErrHeader {
+		t.Errorf("expected error header \"%s\", got %s", expectedErrHeader, err.Header())
+	} else if err.Error() != expectedErrStr {
+		t.Errorf("expected error string %s, got %s", expectedErrStr, err.Error())
+	} else if err.HTMLError() != expectedHTMLErrStr {
+		t.Errorf("expected html error string %s, got %s", expectedErrStr, err.HTMLError())
+	} else if err.Retryable() {
+		t.Errorf("expected retryable = false, got true")
+	}
+}
+
 func TestBuildNotFound(t *testing.T) {
 	buildNumber := "15000.0.0"
 	expectedCode := "404"
 	expectedErrHeader := "Build Not Found"
-	expectedErrStr := fmt.Sprintf("The build associated with input %s cannot be found. Please input a valid build number (example: 13310.1035.0) or a valid image name (example: cos-rc-85-13310-1034-0).", buildNumber)
+	expectedErrStr := strings.Join([]string{
+		"The build associated with input",
+		buildNumber,
+		"cannot be found. It may be possible that the input is either invalid or belongs to a",
+		"pre-Cusky build. If you entered a pre-Cusky build number or image name, note that changelog between",
+		"pre-Cusky and Cusky builds are not supported. Otherwise, please input a valid build number",
+		"(example: 13310.1035.0) or a valid image name (example: cos-rc-85-13310-1034-0).",
+	}, " ")
+	expectedHTMLErrStr := fmt.Sprintf("%s %s %s<br><br>%s %s %s %s",
+		"The build associated with input",
+		buildNumber,
+		"cannot be found.",
+		"It may be possible that either the input is either invalid or belongs to a",
+		"pre-Cusky build. If you entered a pre-Cusky build number or image name, note that changelog between",
+		"pre-Cusky and Cusky builds are not supported. Otherwise, please input a valid build number",
+		"(example: 13310.1035.0) or a valid image name (example: cos-rc-85-13310-1034-0).",
+	)
 	err := BuildNotFound(buildNumber)
 	if err.HTTPCode() != expectedCode {
 		t.Errorf("expected HTTP code %s, got %s", expectedCode, err.HTTPCode())
@@ -99,7 +158,7 @@
 		t.Errorf("expected error header \"%s\", got %s", expectedErrHeader, err.Header())
 	} else if err.Error() != expectedErrStr {
 		t.Errorf("expected error string %s, got %s", expectedErrStr, err.Error())
-	} else if err.HTMLError() != expectedErrStr {
+	} else if err.HTMLError() != expectedHTMLErrStr {
 		t.Errorf("expected html error string %s, got %s", expectedErrStr, err.HTMLError())
 	} else if err.Retryable() {
 		t.Errorf("expected retryable = false, got true")
@@ -127,7 +186,7 @@
 
 func TestCLLandingNotFound(t *testing.T) {
 	clID := "1540"
-	expectedCode := "404"
+	expectedCode := "406"
 	expectedErrHeader := "No Build Found"
 	expectedErrStr := fmt.Sprintf("No build was found containing CL %s.", clID)
 	link := testCLLink(clID, testInstanceURL)