Welcome to the forum. Interesting first post.

Yes, your gun has been re-proofed (between 1904 to 1925). It was originally proofed for black powder as a 12 bore with bore measurements (9 inches from breech) of 13/1 i.e. .719-.728.

Prior to re-proof the bores were honed out to 12 bore and should now be between .729 and .739.

Westley-Richards can no doubt tell you, for a fee, if it was made for a specific customer.

Thanks for the photos. It is a very attractive gun.