Official reworks would have matching numbers on the parts. So either new parts would have been used, parts renumbered as the east germans did or infrequently stamped over the number (you see police reworks like this at times), although usually new parts were used most often.
It is not likely that "parts" were put together during the war. Even in the mid 1940's something reworked would have used new parts. It is "possible" that during war time that several guns were put together, but I would count on that as my number one story
as it is much more liekly that parts were put together over the last 55 years...
Ed