As described in teh story, it WAS in compliance with teh NFA.
Brought in by the lawful heirs of a guy who brought it back from Europe on GI trophy papers. 1968 re-authorization of NFA automatically grandfathered anything that had federal papers stating it was lawfully possessed before then.
There’s a case that is 100% parallel to this one, invloving a widow who tried to sell a Thompson SMG her late husband had stored in the attic. Final outcome was the receipt that the guy bought it from the government as a DEWAT before they required DEWATs to be registered as NFA was 100% in compliance with the NFA — the law only requires that you be able to prove Uncle Sam said it was OK for you to own it (by serial number), to qualify as a pre-1968 registration, which the statute says is sufficient registration under the new NFA. The fact that ATF never got all these disparate pieces of paper entered into the NFA registry doesn’t change that, IF you can prove you posessed it lawfully.
I missed out on I don’t know what (and really don’t want to) from an XGF’s grandmother who turned them in to the smokies but would have given them to me if she’d met me in time. I’m sure if I knew I’d be losing more sleep than I already do.