John,
In 2002, I was furnished a copy of a letter that referenced several Luger documents(blueprints); wood grips, magazine tubes(extruded and folded), spring followers, synthetic black mag bottoms etc etc. The ones I posted references to were only two of the dozen or so documents found and noted in said letter.
The author of the letter(a super heavy) said that the documents were available from another private individual in Oberndorf(I will not say much as I value his privacy) or from the Oberndorf Museum archives. I seriously doubt of an online source, I got the impression it was a in person search in physical Oberndorf archives. This letter is close to 20 years old now.
At one time, there was quite a bit of research in various European archives, this was a small subset I would surmise.
I posted what I did only as a possible lead to the real answer of the original query at the top of this thread. Laminated plasticized grip drawing approved in 39 is information.
I, like others, that purchased VOPO Lugers got some with brown laminated grips. I cannot draw much of an conclusion from just buying a few VOPO Lugers as to originality to said Lugers, but only that is how they showed up in my hands years ago. Looks like the blueprints and their approval would be a bit more concrete in forming a answer to when and how's; at least a starting reference if nothing else. Just my non collecting point of view.
Feel like a trip, I hear it is nice country...............
....I have never been across the Mississippi on my own accord; too old to go now.
Rick