The guns dont have numbers
Now, that's a puzzlement. The Europeans were meticulous about serializing weapons. The P 38 will have a serial number, for example. I have, and have had, beaucoup foreign military weapons; each and every one had or has a serial number.
If the serial numbers have been defaced or removed, now you have a really serious problem, as defacing or removing firearm serial numbers is a Federal felony. The BATFE knows darn well that the P 38, for example, had a serial number. You would have no way to prove it wasn't you, or a family member, that did the deed