Luger stock lugs - Originally fitted to stock?

[A.Mifsin]

Originally Posted by Ron Wood

The "leave the notch alone" in your last comment is what you should do. Four inch barreled Lugers were never issued with a stock, so you shouldn't mess with your S/42. Also pay heed to what Ron posted about the legality of stocks. He is exactly right.

Ron, If 4 inch barrel Lugers were not issued with a stock, what was the reason to produce the Luger with a stock lug ?
Alf