I have seen old sets of locks as supplied to a gunmaker by Stanton or some such and they were nicely shaped and finished (but not fully polished) and the lock plates were of a rough 'generic' shape rather than the exact shape and size as fitted.
The gunmaker would then have filed them exactly to size and shape, applied the exact taper on the edges for a perfect wood to metal fit, made any small modifications to suit the other mechanisms and after the whole gun had been brought together by the actioner (or whosoever that particular maker used for this task) the gun would have been engraved, en suite and then hardened.
This is a grossly simplified version of events but in essence, the locks came 95% completed other than 'finishing'.
And by the way, have a wonderful Christmas!
