Great review man! I am fortunate to have a 1933 commercial PPK and a 1940 commercial PP both in 7.65/32acp. Both are an absolute pleasure to shoot. I have to say that I enjoy shooting the PPK more because the grips fully encompass the metal backstrap and because of this the recoil seems even more tame than the PP. I used to own a Swiss Police PP made in West Germany like yours, outstanding craftsmanship. Definitely try to find a Zella-Mehlis manufactured Walther, to me these are the best quality of all PP series pistols. They have incredible fit and finish, everything feels tight and smooth like glass.
NDS stamp is from the state police of Lower Saxony. en.wikipedia.org/wiki/Lower_Saxony Sometimes when surplusing guns they overstamped that with a big X. Bavarian state police did this for example (their stamp is ByP).
Excellent firearm!!!! I just picked up the R51, this pistol is very nice as well. The takedown is awful but doable, and the recoil is so light. Extremely flat shooting.