More on the NFA database errors
David Codrea goes into it here.
Essentially, it's a federal felony to have an unregistered NFA firearm (machine gun, short barreled rifle or shotgun, etc.). ATF is tasked with maintaining the registry of those. But for decades it's been known that the registry has major omissions. It's been around for 75 years, and thing got lost. The folks actually entering transfers of firearms into it haven't always been the best. Some records were thrown away rather than entered. Wrong serial numbers were entered. Etc..
I once represented a major NFA licensed dealer, Curtis Earl, who was raided on nonexistent grounds. ATF checked his (very large) inventory against their records, and began piling supposedly unregistered guns on the floor. There were dozens of guns in the pile before Curtis pulled out his own records, and showed the agents that he had the registration papers sent by their agency. All the guns were back onto his shelves.