Is it something that came from the factory or was it added later?
Here's a really rough
rule of thumb: If the compensator has a brand name on it (Cutts or?) it could been installed after market. If it doesn't have any markings, then there's a chance it was a factory job.
The RemingtonSociety.com used to have a copy of the old factory ledger with production dates, but it doesn't seem to be available at this time.