The only problem that I can see is in the Wiemar Era navies. These guns can be easily labeled as fakes. I have one that has a P-08 frame and a small cap rear hinge pin. I could explain it and show a prospective buyer, but it would sound like "Sales Talk".
On second thought, we don't even have to go to the Wiemar Era. The 1908 commercial navy Luger has a simular problem. These 1908's, even in the 51000 serial range, had both the long and the short frame.
Big Norm