diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 407481f..d5ef3a5 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -57,8 +57,9 @@ jobs:
           BASE_SHA: ${{ github.event.pull_request.base.sha }}
           HEAD_SHA: ${{ github.event.pull_request.head.sha }}
           PR_TITLE: ${{ github.event.pull_request.title }}
+          COMMIT_CONVENTION_GRANDFATHER: edb0ade331c54f380ae33abe7816c5a92f3a590a
         run: |
-          node scripts/validate-commit-message.mjs --range "$BASE_SHA" "$HEAD_SHA"
+          node scripts/validate-commit-message.mjs --range "$BASE_SHA" "$HEAD_SHA" --grandfather-through "$COMMIT_CONVENTION_GRANDFATHER"
           node scripts/validate-commit-message.mjs --title "$PR_TITLE"
 
       - name: Check changed files for whitespace errors
diff --git a/docs/development-workflow.md b/docs/development-workflow.md
index 0e1b7a1..5ded476 100644
--- a/docs/development-workflow.md
+++ b/docs/development-workflow.md
@@ -36,7 +36,7 @@ Human-authored commits use `<Gitmoji>[<Action>] <imperative subject>`. The prefi
 
 There is no space between the Gitmoji and `[Action]`; exactly one space separates the closing bracket from a non-empty, concise imperative subject. Each commit represents one logical change. For example, `✨[Feat] Add Image to Text OCR` and `✅[Test] Cover OCR cancellation` are valid; `feat: add OCR`, `✨ [Feat] Add OCR`, and `✨[Fix] Add OCR` are invalid.
 
-CI validates non-merge commits introduced by the pull request’s actual base-to-head range and validates the pull-request title with the same structural rule. Technical merge commits are excluded by their multiple-parent topology so normal merge commits remain supported. Published non-conforming history is retained and never rewritten solely for message compliance.
+CI validates non-merge commits introduced by the pull request’s actual base-to-head range and validates the pull-request title with the same structural rule. Technical merge commits are excluded by their multiple-parent topology so normal merge commits remain supported. Published non-conforming history through `edb0ade331c54f380ae33abe7816c5a92f3a590a` is an explicit grandfather boundary: ancestors of that commit are excluded from later ranges, while every human-authored commit after it remains subject to validation. That history is retained and never rewritten solely for message compliance.
 
 ## Production release
 
diff --git a/scripts/validate-commit-message.mjs b/scripts/validate-commit-message.mjs
index c3e0c83..84e181a 100644
--- a/scripts/validate-commit-message.mjs
+++ b/scripts/validate-commit-message.mjs
@@ -38,13 +38,15 @@ function git(argumentsList, cwd) {
   return execFileSync("git", argumentsList, { cwd, encoding: "utf8", stdio: ["ignore", "pipe", "pipe"] }).trim();
 }
 
-export function nonMergeCommits(base, head, cwd = process.cwd()) {
-  const output = git(["rev-list", "--reverse", "--no-merges", `${base}..${head}`], cwd);
+export function nonMergeCommits(base, head, cwd = process.cwd(), grandfatherThrough = null) {
+  const argumentsList = ["rev-list", "--reverse", "--no-merges", `${base}..${head}`];
+  if (grandfatherThrough) argumentsList.push(`^${grandfatherThrough}`);
+  const output = git(argumentsList, cwd);
   return output ? output.split(/\r?\n/) : [];
 }
 
-export function validateCommitRange(base, head, cwd = process.cwd()) {
-  return nonMergeCommits(base, head, cwd).map((sha) => {
+export function validateCommitRange(base, head, cwd = process.cwd(), grandfatherThrough = null) {
+  return nonMergeCommits(base, head, cwd, grandfatherThrough).map((sha) => {
     const subject = git(["show", "-s", "--format=%s", sha], cwd);
     return { sha, subject, ...validateCommitMessage(subject) };
   });
@@ -69,17 +71,19 @@ export function run(argumentsList = process.argv.slice(2), cwd = process.cwd())
     return;
   }
 
-  if (mode === "--range" && values.length === 2) {
-    const results = validateCommitRange(values[0], values[1], cwd);
+  if (mode === "--range" && (values.length === 2 || (values.length === 4 && values[2] === "--grandfather-through"))) {
+    const grandfatherThrough = values[3] || null;
+    const results = validateCommitRange(values[0], values[1], cwd, grandfatherThrough);
     const failures = results.filter((result) => !result.valid);
     if (failures.length) {
       throw new Error(failures.map((failure) => failureText(`commit ${failure.sha}`, failure.subject, failure.reason)).join("\n\n"));
     }
-    console.log(`Validated ${results.length} non-merge commit${results.length === 1 ? "" : "s"} in ${values[0]}..${values[1]}.`);
+    const boundary = grandfatherThrough ? ` after grandfather boundary ${grandfatherThrough}` : "";
+    console.log(`Validated ${results.length} non-merge commit${results.length === 1 ? "" : "s"} in ${values[0]}..${values[1]}${boundary}.`);
     return;
   }
 
-  throw new Error("Usage: node scripts/validate-commit-message.mjs --message <subject> | --title <title> | --range <base-sha> <head-sha>");
+  throw new Error("Usage: node scripts/validate-commit-message.mjs --message <subject> | --title <title> | --range <base-sha> <head-sha> [--grandfather-through <sha>]");
 }
 
 if (process.argv[1] && fileURLToPath(import.meta.url) === process.argv[1]) {
diff --git a/tests/ci-foundation.test.mjs b/tests/ci-foundation.test.mjs
index 4118666..478d19f 100644
--- a/tests/ci-foundation.test.mjs
+++ b/tests/ci-foundation.test.mjs
@@ -21,7 +21,8 @@ assert.match(workflow, /name: Enforce commit and pull request title conventions/
 assert.match(workflow, /BASE_SHA: \$\{\{ github\.event\.pull_request\.base\.sha \}\}/);
 assert.match(workflow, /HEAD_SHA: \$\{\{ github\.event\.pull_request\.head\.sha \}\}/);
 assert.match(workflow, /PR_TITLE: \$\{\{ github\.event\.pull_request\.title \}\}/);
-assert.match(workflow, /node scripts\/validate-commit-message\.mjs --range "\$BASE_SHA" "\$HEAD_SHA"/);
+assert.match(workflow, /COMMIT_CONVENTION_GRANDFATHER: edb0ade331c54f380ae33abe7816c5a92f3a590a/);
+assert.match(workflow, /node scripts\/validate-commit-message\.mjs --range "\$BASE_SHA" "\$HEAD_SHA" --grandfather-through "\$COMMIT_CONVENTION_GRANDFATHER"/);
 assert.match(workflow, /node scripts\/validate-commit-message\.mjs --title "\$PR_TITLE"/);
 assert.match(workflow, /git diff --check/);
 assert.match(workflow, /run: npm ci --ignore-scripts/);
diff --git a/tests/commit-message.test.mjs b/tests/commit-message.test.mjs
index f8304aa..1e4982f 100644
--- a/tests/commit-message.test.mjs
+++ b/tests/commit-message.test.mjs
@@ -81,6 +81,16 @@ try {
   assert.equal(failures.length, 1);
   assert.equal(failures[0].subject, "test: add invalid fixture");
   assert.match(failures[0].sha, /^[0-9a-f]{40}$/);
+
+  fs.writeFileSync(path.join(temporaryRepository, "current.txt"), "current\n");
+  git("add", "current.txt");
+  git("commit", "-q", "-m", "🐛[Fix] Validate commits after enforcement");
+  const currentHead = git("rev-parse", "HEAD");
+  const grandfathered = validateCommitRange(base, currentHead, temporaryRepository, invalidHead);
+  assert.equal(grandfathered.length, 1, "published ancestors through the enforcement boundary are excluded");
+  assert.equal(grandfathered[0].subject, "🐛[Fix] Validate commits after enforcement");
+  assert.equal(grandfathered[0].valid, true);
+  assert.doesNotThrow(() => run(["--range", base, currentHead, "--grandfather-through", invalidHead], temporaryRepository));
 } finally {
   fs.rmSync(temporaryRepository, { recursive: true, force: true });
 }