The doc info on XDCR conflict resolution might be helpful – XDCR Conflict Resolution | Couchbase Docs
So, depending on the conflict resolution you are using (the default on a bucket is revId/sequence number), you can check the metadata of the documents to check the revId, cas values.
Can also check out the below xdcr forum question to see if any of the info there is helpful – Replication problem with Couchbase server 6.6.1