Unnumbered frame

I am in possession of two WW2 era lugers, what I would call transitional lugers or out of sequence meaning lugers assembled by the factory with maybe a toggle or receiver from a different year or era of production but all the same it was produced by Mauser just with a part that may not seem to be of that particular era and time of production. My question,these guns have no serial numbers on the frame. Is there added value to be had here or simply a gun using a serial number from its receiver as it's identifying serial giving it no more value than if it had it on the frame? Any ideas.