First, if it is dewat and is in the system at atf... then not only will the papers be there, but it can be reactivated to class 3 legally. That said I don’t recall if a g43 is select fire or not. Dewat paperwork is like gold!
If not select fire and dewat it can be restored to semi with no paperwork.
In any case if brought home properly, there were forms but if separated from gun they are probably gone. If duplicates were kept I would not know where to start looking.
And millions of guns were brought back in footlockers duffle bags mailed.. not just captured. The us forces made Europeans turn in their weapons. The letter of the law was to turn in military stuff. Many Europeans thought that had to hand over everything. As a result, millions of sporting arms and many priceless guns got handed over... many destroyed. But some enterprising officers and NCOs picked over the good stuff and came home with vast collections. These are still showing up.
Oh to have a time machine.
Cheers, Sirhr