In DocumentSourceShardCheckResumability, we verify that the first entry in each shard's oplog precedes the resume token in order to guarantee that the resumed stream does not skip any events. If we are resuming from a point in time before one of the shards in the cluster was added, then the first entry in that shard's oplog will always be later than the resume token, and will always fail this check. This renders the stream unresumable from any point before the shard was added.