Say coll1 (with uuid1) is sharded and coll2 (with uuid2) is unsharded, and the command {insert: coll1, documents: [{_id: 1}], collectionUUID: uuid2} is issued where the document {_id: 1} belongs on the non-primary shard. Then the returned CollectionUUIDMismatch will erroneously not contain coll2, because it only exists on the primary shard. We should make sure that regardless of which shards are targeted and no matter whether collections are sharded are unsharded, the CollectionUUIDMismatch contains all of the information that it should.