The dbVersion metadata checks cannot be performed because shards (even db-primary shards) are allowed to have a stale notion of the dbVersion – they are not authoritative for it.

For example, when createDatabase finishes, there's no guarantee that the new primary shard will have been made aware of it. The configsvr will do a best effort attempt at telling the primary shard to refresh, but in case of failover this may never be done.