diff --git a/README.md b/README.md
index 9deecf7..dbf02a7 100644
--- a/README.md
+++ b/README.md
@@ -9,7 +9,7 @@ This action compares dependencies between your base branch and current branch, a
 - 🔒 **Package trust levels** - Detects decreases in package trust levels (provenance and trusted publisher status)
 - 📈 **Dependency growth** - Warns when dependency count increases significantly
 - 📦 **Install size** - Warns when package size increases significantly
-- 🔄 **Duplicate versions** - Detects packages with multiple versions installed
+- 🔄 **Duplicate versions** - Detects packages which gain newly introduced duplicate versions
 - ⚠️ **Module replacements** - Identifies new packages that have community-recommended alternatives
 
 ## Usage
@@ -44,7 +44,7 @@ jobs:
 | `pr-number`            | The number of the pull request to comment on                                                                               | Yes      | `${{ github.event.pull_request.number }}` |
 | `dependency-threshold` | Threshold for warning about significant increase in number of dependencies                                                 | No       | `10`                                      |
 | `size-threshold`       | Threshold (in bytes) for warning about significant increase in package size                                                | No       | `100000`                                  |
-| `duplicate-threshold`  | Threshold for warning about packages with multiple versions                                                                | No       | `1`                                       |
+| `duplicate-threshold`  | Threshold for warning about packages which gain newly introduced duplicate versions                                        | No       | `1`                                       |
 | `base-packages`        | Glob pattern for base branch pack files (e.g., `"./base-packs/*.tgz"`)                                                     | No       | None                                      |
 | `source-packages`      | Glob pattern for source branch pack files (e.g., `"./source-packs/*.tgz"`)                                                 | No       | None                                      |
 | `pack-size-threshold`  | Threshold (in bytes) for warning about significant increase in total pack size. Set to `-1` to always report size changes. | No       | `50000`                                   |
diff --git a/action.yml b/action.yml
index 1e5fc1f..eca713e 100644
--- a/action.yml
+++ b/action.yml
@@ -37,7 +37,7 @@ inputs:
     required: false
     default: '50000'
   duplicate-threshold:
-    description: 'Threshold for warning about packages with multiple versions'
+    description: 'Threshold for warning about packages which gain newly introduced duplicate versions'
     required: false
     default: '1'
   detect-replacements:
diff --git a/build/main.js b/build/main.js
index b71b55a..c4e08df 100644
--- a/build/main.js
+++ b/build/main.js
@@ -24615,11 +24615,12 @@ function computeParentPaths(lockfile, duplicateDependencyNames, dependencyMap) {
   traverse(lockfile.root, visitor);
   return parentPaths;
 }
-function scanForDuplicates(messages, threshold, dependencyMap, lockfilePath, lockfile) {
+function scanForDuplicates(messages, threshold, dependencyMap, baseDependencyMap, lockfilePath, lockfile) {
   const duplicateRows = [];
   const duplicateDependencyNames = /* @__PURE__ */ new Set();
   for (const [packageName, currentVersionSet] of dependencyMap) {
-    if (currentVersionSet.size > threshold) {
+    const baseVersionCount = baseDependencyMap.get(packageName)?.size ?? 0;
+    if (currentVersionSet.size > threshold && currentVersionSet.size > baseVersionCount) {
       duplicateDependencyNames.add(packageName);
     }
   }
@@ -24673,7 +24674,7 @@ function scanForDuplicates(messages, threshold, dependencyMap, lockfilePath, loc
 
 \u{1F4A1} To find out what depends on a specific package, run: \`${exampleCommand}\`` : "";
     messages.push(
-      `## \u26A0\uFE0F Duplicate Dependencies (found: ${duplicateRows.length}, threshold: ${threshold})
+      `## \u26A0\uFE0F New Duplicate Dependencies (found: ${duplicateRows.length}, threshold: ${threshold})
 
 | \u{1F4E6} Package | \u{1F4CB} Versions |
 | --- | --- |
@@ -25129,6 +25130,7 @@ async function analyzeAndComment() {
       messages,
       duplicateThreshold,
       currentDeps,
+      baseDeps,
       lockfilePath,
       parsedCurrentLock
     );
diff --git a/src/checks/duplicates.ts b/src/checks/duplicates.ts
index 80038a5..5c302ec 100644
--- a/src/checks/duplicates.ts
+++ b/src/checks/duplicates.ts
@@ -56,6 +56,7 @@ export function scanForDuplicates(
   messages: string[],
   threshold: number,
   dependencyMap: Map<string, Set<string>>,
+  baseDependencyMap: Map<string, Set<string>>,
   lockfilePath: string,
   lockfile: ParsedLockFile
 ): void {
@@ -63,7 +64,11 @@ export function scanForDuplicates(
   const duplicateDependencyNames = new Set<string>();
 
   for (const [packageName, currentVersionSet] of dependencyMap) {
-    if (currentVersionSet.size > threshold) {
+    const baseVersionCount = baseDependencyMap.get(packageName)?.size ?? 0;
+    if (
+      currentVersionSet.size > threshold &&
+      currentVersionSet.size > baseVersionCount
+    ) {
       duplicateDependencyNames.add(packageName);
     }
   }
@@ -126,7 +131,7 @@ export function scanForDuplicates(
       ? `\n\n💡 To find out what depends on a specific package, run: \`${exampleCommand}\``
       : '';
     messages.push(
-      `## ⚠️ Duplicate Dependencies (found: ${duplicateRows.length}, threshold: ${threshold})
+      `## ⚠️ New Duplicate Dependencies (found: ${duplicateRows.length}, threshold: ${threshold})
 
 | 📦 Package | 📋 Versions |
 | --- | --- |
diff --git a/src/main.ts b/src/main.ts
index d34fd47..24d664b 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -174,6 +174,7 @@ async function analyzeAndComment(): Promise<void> {
       messages,
       duplicateThreshold,
       currentDeps,
+      baseDeps,
       lockfilePath,
       parsedCurrentLock
     );
diff --git a/test/checks/__snapshots__/duplicates_test.ts.snap b/test/checks/__snapshots__/duplicates_test.ts.snap
index f899c29..4d4f3eb 100644
--- a/test/checks/__snapshots__/duplicates_test.ts.snap
+++ b/test/checks/__snapshots__/duplicates_test.ts.snap
@@ -1,8 +1,20 @@
 // Vitest Snapshot v1, https://vitest.dev/guide/snapshot.html
 
+exports[`scanForDuplicates > should only report packages with more versions than the base 1`] = `
+[
+  "## ⚠️ New Duplicate Dependencies (found: 1, threshold: 1)
+
+| 📦 Package | 📋 Versions |
+| --- | --- |
+| package-a | <details><summary>2 versions</summary><br><ul><li>root-package@1.0.0<ul><li>**package-a@1.0.0**</li></ul></li></ul><br><ul><li>root-package@1.0.0<ul><li>package-b@3.0.0<ul><li>**package-a@1.1.0**</li></ul></li></ul></li></ul><br></details> |
+
+💡 To find out what depends on a specific package, run: \`npm ls example-package\`",
+]
+`;
+
 exports[`scanForDuplicates > should report duplicates when threshold is exceeded 1`] = `
 [
-  "## ⚠️ Duplicate Dependencies (found: 1, threshold: 1)
+  "## ⚠️ New Duplicate Dependencies (found: 1, threshold: 1)
 
 | 📦 Package | 📋 Versions |
 | --- | --- |
@@ -14,7 +26,7 @@ exports[`scanForDuplicates > should report duplicates when threshold is exceeded
 
 exports[`scanForDuplicates > should truncate long parent paths in the report 1`] = `
 [
-  "## ⚠️ Duplicate Dependencies (found: 1, threshold: 1)
+  "## ⚠️ New Duplicate Dependencies (found: 1, threshold: 1)
 
 | 📦 Package | 📋 Versions |
 | --- | --- |
diff --git a/test/checks/duplicates_test.ts b/test/checks/duplicates_test.ts
index f133055..082baa7 100644
--- a/test/checks/duplicates_test.ts
+++ b/test/checks/duplicates_test.ts
@@ -28,6 +28,7 @@ describe('scanForDuplicates', () => {
       messages,
       threshold,
       dependencyMap,
+      new Map(),
       lockfilePath,
       lockfile
     );
@@ -84,6 +85,7 @@ describe('scanForDuplicates', () => {
       messages,
       threshold,
       dependencyMap,
+      new Map(),
       lockfilePath,
       lockfile
     );
@@ -140,6 +142,7 @@ describe('scanForDuplicates', () => {
       messages,
       threshold,
       dependencyMap,
+      new Map(),
       lockfilePath,
       lockfile
     );
@@ -203,6 +206,189 @@ describe('scanForDuplicates', () => {
       messages,
       threshold,
       dependencyMap,
+      new Map(),
+      lockfilePath,
+      lockfile
+    );
+
+    expect(messages).toMatchSnapshot();
+  });
+
+  it('should not report duplicates which already exist in the base', () => {
+    const messages: string[] = [];
+    const threshold = 1;
+    const dependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.1.0'])]
+    ]);
+    const baseDependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.1.0'])]
+    ]);
+    const lockfilePath = 'package-lock.json';
+    const lockfile: ParsedLockFile = {
+      type: 'npm',
+      packages: [],
+      root: {
+        name: 'root-package',
+        version: '1.0.0',
+        dependencies: [],
+        devDependencies: [],
+        optionalDependencies: [],
+        peerDependencies: []
+      }
+    };
+
+    scanForDuplicates(
+      messages,
+      threshold,
+      dependencyMap,
+      baseDependencyMap,
+      lockfilePath,
+      lockfile
+    );
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should not report duplicates when the version count is unchanged', () => {
+    const messages: string[] = [];
+    const threshold = 1;
+    const dependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.2.0'])]
+    ]);
+    const baseDependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.1.0'])]
+    ]);
+    const lockfilePath = 'package-lock.json';
+    const lockfile: ParsedLockFile = {
+      type: 'npm',
+      packages: [],
+      root: {
+        name: 'root-package',
+        version: '1.0.0',
+        dependencies: [],
+        devDependencies: [],
+        optionalDependencies: [],
+        peerDependencies: []
+      }
+    };
+
+    scanForDuplicates(
+      messages,
+      threshold,
+      dependencyMap,
+      baseDependencyMap,
+      lockfilePath,
+      lockfile
+    );
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should not report duplicates when versions are removed', () => {
+    const messages: string[] = [];
+    const threshold = 1;
+    const dependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.1.0'])]
+    ]);
+    const baseDependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.1.0', '1.2.0'])]
+    ]);
+    const lockfilePath = 'package-lock.json';
+    const lockfile: ParsedLockFile = {
+      type: 'npm',
+      packages: [],
+      root: {
+        name: 'root-package',
+        version: '1.0.0',
+        dependencies: [],
+        devDependencies: [],
+        optionalDependencies: [],
+        peerDependencies: []
+      }
+    };
+
+    scanForDuplicates(
+      messages,
+      threshold,
+      dependencyMap,
+      baseDependencyMap,
+      lockfilePath,
+      lockfile
+    );
+
+    expect(messages).toHaveLength(0);
+  });
+
+  it('should only report packages with more versions than the base', () => {
+    const messages: string[] = [];
+    const threshold = 1;
+    const dependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0', '1.1.0'])],
+      ['package-c', new Set(['2.0.0', '2.1.0'])]
+    ]);
+    const baseDependencyMap = new Map<string, Set<string>>([
+      ['package-a', new Set(['1.0.0'])],
+      ['package-c', new Set(['2.0.0', '2.1.0'])]
+    ]);
+    const lockfilePath = 'package-lock.json';
+    const packageA: ParsedDependency = {
+      name: 'package-a',
+      version: '1.0.0',
+      dependencies: [],
+      devDependencies: [],
+      optionalDependencies: [],
+      peerDependencies: []
+    };
+    const packageAAlt: ParsedDependency = {
+      name: 'package-a',
+      version: '1.1.0',
+      dependencies: [],
+      devDependencies: [],
+      optionalDependencies: [],
+      peerDependencies: []
+    };
+    const packageC: ParsedDependency = {
+      name: 'package-c',
+      version: '2.0.0',
+      dependencies: [],
+      devDependencies: [],
+      optionalDependencies: [],
+      peerDependencies: []
+    };
+    const packageCAlt: ParsedDependency = {
+      name: 'package-c',
+      version: '2.1.0',
+      dependencies: [],
+      devDependencies: [],
+      optionalDependencies: [],
+      peerDependencies: []
+    };
+    const packageB: ParsedDependency = {
+      name: 'package-b',
+      version: '3.0.0',
+      dependencies: [packageAAlt, packageCAlt],
+      devDependencies: [],
+      optionalDependencies: [],
+      peerDependencies: []
+    };
+    const lockfile: ParsedLockFile = {
+      type: 'npm',
+      packages: [packageA, packageAAlt, packageB, packageC, packageCAlt],
+      root: {
+        name: 'root-package',
+        version: '1.0.0',
+        dependencies: [packageA, packageB, packageC],
+        devDependencies: [],
+        optionalDependencies: [],
+        peerDependencies: []
+      }
+    };
+
+    scanForDuplicates(
+      messages,
+      threshold,
+      dependencyMap,
+      baseDependencyMap,
       lockfilePath,
       lockfile
     );