diff --git a/packages/cultcache-ts/src/store-format.ts b/packages/cultcache-ts/src/store-format.ts
index 193abc03..4efab504 100644
--- a/packages/cultcache-ts/src/store-format.ts
+++ b/packages/cultcache-ts/src/store-format.ts
@@ -16,16 +16,12 @@ const PERSISTED_RECORD_SLOTS = 4;
 const STORE_SLOTS = 3;
 
 /**
- * True for a v1 or v3 snapshot, false for anything that is not a CultCache store header (the legacy
- * envelope array). Any other `cultcache.store.*` header is refused by name.
+ * True for a decoded array that leads with a `cultcache.store.*` stamp, false for the legacy envelope array. It judges the
+ * shape only: the verdict on the stamp is {@link refuseUnreadStoreBytes}, which a reader calls on the bytes before it decodes,
+ * so the stamp of a decoded array it is given is one this runtime reads.
  */
 export function isStoreSnapshot(decoded: unknown): decoded is [StoreFormat, ...unknown[]] {
-  if (!Array.isArray(decoded) || typeof decoded[0] !== "string" || !decoded[0].startsWith(STORE_FORMAT_PREFIX)) {
-    return false;
-  }
-
-  refuseUnreadFormat(decoded[0]);
-  return true;
+  return Array.isArray(decoded) && typeof decoded[0] === "string" && decoded[0].startsWith(STORE_FORMAT_PREFIX);
 }
 
 /**
diff --git a/packages/cultcache-ts/test/cult-cache.test.ts b/packages/cultcache-ts/test/cult-cache.test.ts
index 11043959..02324273 100644
--- a/packages/cultcache-ts/test/cult-cache.test.ts
+++ b/packages/cultcache-ts/test/cult-cache.test.ts
@@ -2121,9 +2121,17 @@ test("a store's header is judged from its first bytes, in every MessagePack arra
   assert.equal(headerRefused(storeStart([0x91], `cultcache.store.v4${"x".repeat(13)}`, "fix")), true);
   assert.equal(headerRefused(storeStart([0x91], `cultcache.store.v4${"x".repeat(300)}`, "16")), true);
   assert.equal(headerRefused(storeStart([0x91], `cultcache.store.v4${"x".repeat(300)}`, "32")), true);
-  // A view into a larger buffer is read from its own start.
-  const padded = new Uint8Array([9, 9, ...storeStart([0x91], "cultcache.store.v4", "fix")]);
-  assert.equal(headerRefused(padded.subarray(2)), true);
+  // A view into a larger buffer is read from its own start, in every form that reads a length through the DataView.
+  for (const lead of leads) {
+    for (const form of ["fix", "8", "16", "32"] as const) {
+      const padded = new Uint8Array([7, 7, 7, ...storeStart(lead, "cultcache.store.v4", form)]);
+      assert.equal(padded.subarray(3).byteOffset, 3);
+      assert.equal(headerRefused(padded.subarray(3)), true, `${lead} ${form} v4 at a byte offset`);
+    }
+  }
+  // The stamp is judged as written: a stamp with a space is not the stamp this runtime reads, and not one it ignores.
+  assert.equal(headerRefused(storeStart([0x91], "cultcache.store.v3 ", "fix")), true, "a v3 stamp with a trailing space is a header this runtime does not read");
+  assert.equal(headerRefused(storeStart([0x91], " cultcache.store.v4", "fix")), false, "a leading space makes it no cultcache.store.* header");
 });
 
 test("bytes with no readable store stamp are not refused", () => {