Another indicator of a DDR rework is the size of the two digit serial number fragment of each small part. The Germans, prior to 1946, tended to stamp these numbers with dies that produced digits that were two millimeters in height. The DDR used dies that produced larger (four millimeters) digits.
I had to look a bit to find a photo that will (I hope) illustrate the difference. The picture just below is of a DDR reworked 1939/42 Luger that was sent to Yemen as Warsaw pact military aid (circa 1960).
This pistol has a replacement side plate with the 4mm digits common to DDR rework parts. The size difference to the number on the (original) locking block are fairly easy to see in this photo:
Giving credit where credit is due, I initially learned of the difference in font sizes from one of Dieter Marschall's works. I cannot remember which work and so cannot do a better citation.