diff --git a/lib/rules/template-require-iframe-title.js b/lib/rules/template-require-iframe-title.js
index fb55c97966..2f5240bd5a 100644
--- a/lib/rules/template-require-iframe-title.js
+++ b/lib/rules/template-require-iframe-title.js
@@ -10,7 +10,14 @@ module.exports = {
     },
     schema: [],
     messages: {
+      // Split from a single `missingTitle` into four messageIds aligned with
+      // upstream ember-template-lint, providing richer diagnostic detail.
       missingTitle: '<iframe> elements must have a unique title property.',
+      emptyTitle: '<iframe> elements must have a unique title property.',
+      dynamicFalseTitle: '<iframe> elements must have a unique title property.',
+      duplicateTitleFirst: 'This title is not unique. #{{index}}',
+      duplicateTitleOther:
+        '<iframe> elements must have a unique title property. Value title="{{title}}" already used for different iframe. #{{index}}',
     },
     originallyFrom: {
       name: 'ember-template-lint',
@@ -20,7 +27,12 @@ module.exports = {
     },
   },
   create(context) {
+    // Each entry: { value, node, index }
+    //  - value: trimmed title string
+    //  - node: original element node for the first occurrence
+    //  - index: duplicate-group index (1-based), assigned lazily on collision
     const knownTitles = [];
+    let nextDuplicateIndex = 1;
 
     return {
       GlimmerElementNode(node) {
@@ -47,14 +59,36 @@ module.exports = {
             case 'GlimmerTextNode': {
               const value = titleAttr.value.chars.trim();
               if (value.length === 0) {
-                context.report({ node, messageId: 'missingTitle' });
+                context.report({ node, messageId: 'emptyTitle' });
               } else {
-                // Check for duplicate titles
-                const existingIdx = knownTitles.findIndex(([val]) => val === value);
-                if (existingIdx === -1) {
-                  knownTitles.push([value, node]);
+                // Check for duplicate titles. Upstream reports BOTH the
+                // first and the current occurrence of a duplicated title
+                // on every collision, sharing a `#N` index so users can
+                // correlate them. For three or more duplicates the first
+                // occurrence is therefore re-reported once per collision.
+                const existing = knownTitles.find((entry) => entry.value === value);
+                if (existing) {
+                  if (existing.index === null) {
+                    existing.index = nextDuplicateIndex++;
+                  }
+                  const index = existing.index;
+
+                  // Report on the first occurrence on every collision,
+                  // matching upstream ember-template-lint behavior.
+                  context.report({
+                    node: existing.node,
+                    messageId: 'duplicateTitleFirst',
+                    data: { index: String(index) },
+                  });
+
+                  // Report on the current (duplicate) occurrence.
+                  context.report({
+                    node,
+                    messageId: 'duplicateTitleOther',
+                    data: { title: titleAttr.value.chars, index: String(index) },
+                  });
                 } else {
-                  context.report({ node, messageId: 'missingTitle' });
+                  knownTitles.push({ value, node, index: null });
                 }
               }
               break;
@@ -62,7 +96,7 @@ module.exports = {
             case 'GlimmerMustacheStatement': {
               // title={{false}} → BooleanLiteral false is invalid
               if (titleAttr.value.path?.type === 'GlimmerBooleanLiteral') {
-                context.report({ node, messageId: 'missingTitle' });
+                context.report({ node, messageId: 'dynamicFalseTitle' });
               }
               break;
             }
@@ -74,7 +108,7 @@ module.exports = {
                 parts[0].type === 'GlimmerMustacheStatement' &&
                 parts[0].path?.type === 'GlimmerBooleanLiteral'
               ) {
-                context.report({ node, messageId: 'missingTitle' });
+                context.report({ node, messageId: 'dynamicFalseTitle' });
               }
               break;
             }
diff --git a/tests/lib/rules/template-require-iframe-title.js b/tests/lib/rules/template-require-iframe-title.js
index 929bf786f1..9f67323184 100644
--- a/tests/lib/rules/template-require-iframe-title.js
+++ b/tests/lib/rules/template-require-iframe-title.js
@@ -28,18 +28,61 @@ ruleTester.run('template-require-iframe-title', rule, {
     {
       code: '<template><iframe title=""></iframe></template>',
       output: null,
-      errors: [{ messageId: 'missingTitle' }],
+      errors: [{ messageId: 'emptyTitle' }],
     },
 
     {
+      // Upstream reports BOTH occurrences with a shared `#N` index.
       code: '<template><iframe title="foo" /><iframe title="foo" /></template>',
       output: null,
-      errors: [{ messageId: 'missingTitle' }],
+      errors: [
+        { message: 'This title is not unique. #1' },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+      ],
     },
     {
+      // Three duplicates → upstream re-reports the first occurrence on every
+      // collision, so iframe #1 is flagged twice (once per later collision)
+      // and iframes #2 and #3 are each flagged once. ESLint sorts by source
+      // location, so the two first-occurrence reports (same location) come
+      // before the two later occurrences.
+      code: '<template><iframe title="foo" /><iframe title="foo" /><iframe title="foo" /></template>',
+      output: null,
+      errors: [
+        { message: 'This title is not unique. #1' },
+        { message: 'This title is not unique. #1' },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+      ],
+    },
+    {
+      // Two distinct duplicate groups → 4 reports, indices #1 and #2.
+      // ESLint sorts errors by source location; the two "first-occurrence"
+      // reports attach to the first two iframes and so precede the two
+      // "other-occurrence" reports attached to the later iframes.
       code: '<template><iframe title="foo" /><iframe title="boo" /><iframe title="foo" /><iframe title="boo" /></template>',
       output: null,
-      errors: [{ messageId: 'missingTitle' }, { messageId: 'missingTitle' }],
+      errors: [
+        { message: 'This title is not unique. #1' },
+        { message: 'This title is not unique. #2' },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="boo" already used for different iframe. #2',
+        },
+      ],
     },
     {
       code: '<template><iframe src="12" /></template>',
@@ -49,17 +92,17 @@ ruleTester.run('template-require-iframe-title', rule, {
     {
       code: '<template><iframe src="12" title={{false}} /></template>',
       output: null,
-      errors: [{ messageId: 'missingTitle' }],
+      errors: [{ messageId: 'dynamicFalseTitle' }],
     },
     {
       code: '<template><iframe src="12" title="{{false}}" /></template>',
       output: null,
-      errors: [{ messageId: 'missingTitle' }],
+      errors: [{ messageId: 'dynamicFalseTitle' }],
     },
     {
       code: '<template><iframe src="12" title="" /></template>',
       output: null,
-      errors: [{ messageId: 'missingTitle' }],
+      errors: [{ messageId: 'emptyTitle' }],
     },
   ],
 });
@@ -84,14 +127,46 @@ hbsRuleTester.run('template-require-iframe-title', rule, {
     {
       code: '<iframe title="foo" /><iframe title="foo" />',
       output: null,
-      errors: [{ message: '<iframe> elements must have a unique title property.' }],
+      errors: [
+        { message: 'This title is not unique. #1' },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+      ],
+    },
+    {
+      // Three duplicates: upstream re-reports the first occurrence on every
+      // collision, so iframe #1 is flagged twice and each later iframe once.
+      code: '<iframe title="foo" /><iframe title="foo" /><iframe title="foo" />',
+      output: null,
+      errors: [
+        { message: 'This title is not unique. #1' },
+        { message: 'This title is not unique. #1' },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+      ],
     },
     {
       code: '<iframe title="foo" /><iframe title="boo" /><iframe title="foo" /><iframe title="boo" />',
       output: null,
       errors: [
-        { message: '<iframe> elements must have a unique title property.' },
-        { message: '<iframe> elements must have a unique title property.' },
+        { message: 'This title is not unique. #1' },
+        { message: 'This title is not unique. #2' },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="foo" already used for different iframe. #1',
+        },
+        {
+          message:
+            '<iframe> elements must have a unique title property. Value title="boo" already used for different iframe. #2',
+        },
       ],
     },
     {