diff --git a/lib/restamp.ts b/lib/restamp.ts
index 8d31957a2..060a53cf9 100644
--- a/lib/restamp.ts
+++ b/lib/restamp.ts
@@ -183,7 +183,11 @@ function planVersions(o: RestampOptions, loaded: LoadedPolicy, policyLabel: stri
     try { q = JSON.parse(r.stdout ?? ''); } catch {}
     const usable = r.status === 0 && q && typeof q.version === 'string' && parseVersion(q.version) && (q.offline === false || q.fallback === 'git');
     newVersion = usable ? q.version : bumped(atBase.version, level);
-    claims = usable ? `read (claim-at-open; queue ${JSON.stringify(q.claimed ?? q.queue ?? [])})` : 'unverified (claim-at-open; gstack-next-version unusable, local arithmetic)';
+    const queue = JSON.stringify(q?.claimed ?? q?.queue ?? []);
+    const unknown = (Array.isArray(q?.unknown_claims) ? q.unknown_claims : []).map((n: unknown) => `#${n}`).join(', ') || 'some open PRs';
+    claims = !usable ? 'unverified (claim-at-open; gstack-next-version unusable, local arithmetic)'
+      : q.complete === false ? `incomplete (claim-at-open; the VERSION claims of PR ${unknown} are unknown, so ${q.version} is provisional and may collide; rerun, then ask the coordinator before stamping; queue ${queue})`
+      : `read (claim-at-open; queue ${queue})`;
   }
   // The branch's own tentative stamp: its VERSION when it moved past base; else nothing (mentions come from the lines it added).
   const branchStamp = oldVersion !== atBase.version ? oldVersion : null;
diff --git a/test/gstack-restamp-queue.test.ts b/test/gstack-restamp-queue.test.ts
index 4120dc44a..dcac80407 100644
--- a/test/gstack-restamp-queue.test.ts
+++ b/test/gstack-restamp-queue.test.ts
@@ -162,6 +162,30 @@ describe('three PRs, reordered twice, zero manual edits', () => {
     const forced = restamp(repo, ['--next', '--dry-run', '--queue-mode', 'stamp-at-merge']);
     expect(forced.out).toContain('claims: ignored (stamp-at-merge)');
   });
+
+  test('claim-at-open with an unknown claim says incomplete, names the PR and never says read', () => {
+    const repo = fixture({ policy: { ...BASE_POLICY, queue_mode: 'claim-at-open' }, prefix: 'gstack-restamp-github.com-' });
+    makePr(repo, 'pr-a');
+    const shim = path.join(repo.root, 'gh-unknown-claim');
+    fs.mkdirSync(shim);
+    const list = JSON.stringify([41, 42].map(n => ({ number: n, headRefName: `pr-${n}`, headRepositoryOwner: { login: 'o' }, url: `https://github.com/o/r/pull/${n}`, isDraft: false })));
+    fs.writeFileSync(path.join(shim, 'gh'), [
+      '#!/bin/sh',
+      'case "$*" in',
+      `  "pr list --state open --base main --limit 200 --json number,headRefName,headRepositoryOwner,url,isDraft") printf '%s\\n' '${list}'; exit 0 ;;`,
+      "  \"repo view --json owner -q .owner.login\") echo o; exit 0 ;;",
+      `  "api repos/{owner}/{repo}/contents/VERSION?ref=pr-41 -q .content") echo '${Buffer.from('1.2.5.0\n').toString('base64')}'; exit 0 ;;`,
+      "  \"api repos/{owner}/{repo}/contents/VERSION?ref=pr-42 -q .content\") echo 'gh: Server Error (HTTP 502)' >&2; exit 1 ;;",
+      'esac',
+      'exit 2',
+      '',
+    ].join('\n'), { mode: 0o755 });
+    const r = restamp(repo, ['--next', '--dry-run'], { PATH: `${shim}:${process.env.PATH ?? ''}` });
+    expect(r.status, r.err).toBe(EXIT.ok);
+    expect(r.out).toContain('STAMP_VERSION: 1.2.6.0');
+    expect(r.out).toContain('claims: incomplete (claim-at-open; the VERSION claims of PR #42 are unknown, so 1.2.6.0 is provisional and may collide; rerun, then ask the coordinator before stamping; queue [');
+    expect(r.out).not.toMatch(/^claims: read/m);
+  });
 });
 
 describe('journal and injected failures', () => {