ATF corrected my serial number on one SBS, many years ago. I didn't include the few letters of the alphabet that I thought were a prefix to the numbers, but apparently they were part and parcel with the number itself. ATF just amended my Form 1 and approved it. Of course that was back in the day before everybody and his brother decided to get into short barreled shoulder-fired guns and silencers. ATF was not so overworked back then.
