Since the collection's timestamp is now a mandatory field in the global catalog, under this ticket we can get rid of the epoch in the merge (1 , 2) and split (1, 2) paths from the catalog manager backing functions..

This change should be introduced in a release following the inclusion of SERVER-104703 in the latest LTS. For example, if SERVER-104703 is incorporated into v9.0.0, this change can be scheduled for v9.1 or a subsequent version.