SQL Server: How does Uniquifier work with Replication?
Replication requires a primary key constraint on the replicated tables, not a clustered index. Primary key constraints enforce uniqueness. If you have more than one publisher to the same subscriber, you'll need to ensure that there are no collisions. This is often done with identity columns. For instance, one server would use negative numbers, the other server would use positive numbers.

If you also have a non-unique clustered index, the uniqifier doesn't get transferred as it's not part of the INSERT/UPDATE/DELETE command. The uniquifier value will be added on the subscriber and would be different than the value on the publisher.