Hey, I also remember a .357 flattop with an overstamped number on the end..don't remember the number now...10xxx range or 15xxx range or something, but always thought it could be one of those unprovable things.
I've also had reported an M77 s/n 70- 4478D that would otherwise appear to have been rollmarked without the third digit of the serial number, the one after the dash. But after the dash could be seen the bottom line of a number one that was in-line with the tops of the other digits, a case of the numbering digit advanced too far around to impress the whole number into the metal. That gun was shipped though as a "D" gun, duplicating serial number 70-04478.
I can also say that there were a lot of Ruger's about the time period (all models) of the S47 in question where the digits were North or South of where they should be (really sloppy looking).
Chet15