Serial number?

Why was this rifle's serial number changed? From what I can tell so far this 1918 NRF got a new barrel in 1938. Sometime later it was rebuilt, renumbered (bolt & nosecap, too), heavily greased and stored, then found it's way into my grubby paws. Possibly an inventory thing? Could it have something to do with the Irish Free State marks on the receiver and barrel? Oddly, it has a greasy piling swivel.

It is an Irish Enfield. The double F on the Nock's form is the Irish ownership mark. After WW I, Britain sold SMLEs to Ireland. They were checked and refurbished as necessary and re-numbered. That is why one # is crossed out and another added.

Aha! I wasn't aware that the practice extended past the 1920's. Thanks.