diff --git a/src/release-sync.ts b/src/release-sync.ts
index b176040..9afbee4 100644
--- a/src/release-sync.ts
+++ b/src/release-sync.ts
@@ -220,7 +220,7 @@ async function listSyncedVersions(prisma: PrismaClient, type: ReleaseType): Prom
   return new Set(releases.map(release => release.version));
 }
 
-async function releaseExists(
+export async function releaseExists(
   prisma: PrismaClient,
   type: ReleaseType,
   version: string,
diff --git a/src/releases.ts b/src/releases.ts
index 30310fd..da98e0c 100644
--- a/src/releases.ts
+++ b/src/releases.ts
@@ -1,7 +1,7 @@
 import { Request, Response } from "express";
 import { prisma } from "./db";
 import { BadRequestError, ConflictError, InternalServerError, NotFoundError } from "./errors";
-import type { ReleaseSyncRunner } from "./release-sync";
+import { releaseExists, type ReleaseSyncRunner } from "./release-sync";
 import semver from "semver";
 
 import { GetObjectCommand, ListObjectsV2Command } from "@aws-sdk/client-s3";
@@ -734,8 +734,10 @@ const syncBodySchema = z
 /**
  * POST /releases/sync: register every stable R2 version missing from the DB
  * and answer with the per-outcome counts. With `{ type, version }` in the
- * body, that one version skips the settle window: the caller vouches its
- * last object is written. Every other version keeps it.
+ * body, that one version skips the settle window (the caller vouches its
+ * last object is written) and the answer adds `registered`: whether a row
+ * for it exists once the run is over, whichever run created it. The counts
+ * alone cannot say that, since they cover every version scanned.
  */
 export function Sync(runner: ReleaseSyncRunner) {
   return async (req: Request, res: Response) => {
@@ -744,6 +746,10 @@ export function Sync(runner: ReleaseSyncRunner) {
     if (stats === "busy") {
       throw new ConflictError("A release sync is already in progress");
     }
-    return res.json(stats);
+    if (!settled) {
+      return res.json(stats);
+    }
+    const registered = await releaseExists(prisma, settled.type, settled.version);
+    return res.json({ ...stats, registered });
   };
 }
diff --git a/test/sync-releases.test.ts b/test/sync-releases.test.ts
index 3d340d4..32c9710 100644
--- a/test/sync-releases.test.ts
+++ b/test/sync-releases.test.ts
@@ -546,7 +546,9 @@ describe("Sync handler", () => {
 
     await Sync(newRunner())(request({ type: "app", version: FRESH_VERSION }), res);
 
-    expect(res.json).toHaveBeenCalledWith(expect.objectContaining({ created: 1, uploading: 1 }));
+    expect(res.json).toHaveBeenCalledWith(
+      expect.objectContaining({ created: 1, uploading: 1, registered: true }),
+    );
     expect(
       await testPrisma.release.findUnique({
         where: { version_type: { version: FRESH_VERSION, type: "app" } },
@@ -566,6 +568,16 @@ describe("Sync handler", () => {
     await Sync(newRunner())(request(), res);
 
     expect(res.json).toHaveBeenCalledWith(expect.objectContaining({ created: 0, uploading: 2 }));
+    expect(res.json).not.toHaveBeenCalledWith(expect.objectContaining({ registered: expect.anything() }));
+  });
+
+  it("answers registered: false when the named version is not on R2", async () => {
+    mockS3ListVersions("app", []);
+    const res = response();
+
+    await Sync(newRunner())(request({ type: "app", version: "9.9.99" }), res);
+
+    expect(res.json).toHaveBeenCalledWith(expect.objectContaining({ created: 0, registered: false }));
   });
 
   it.each([