Restamped suffix

[zinfull]

I own a 1936 s/42 which has been worked on in its interesting life. Some person stamped the letter "a" over the "i" on the frame and also stamped the reciever with an "a". The gun only has a few mismatch numbers in the small parts.
Why would this happen? I admit that having the only 1936 s/42 in the "a" suffix is rare, but it is hard to verify.