Dave
That was
Don, not
Ron, that posted the photo of the Luger marked 1920.
"In fact I have seen examples where the "grooves" do not match from side to side"...those "examples" didn't leave the factory that way, Lugers are symmetrical.
"Interestingly enough I have drawings of a horizontal groove cut in the top front edge of the slide (forward of where you see 1920 on your gun) that does not appear to have any use"...that groove was to accommodate the rear sight of a LP08 ("Artillery") Luger. Obviously the drawings you saw were of a LP08 that was rebarreled and no longer had that rear sight or was of an Erfurt Arsenal made Luger produced after 1914, all of which were made with that groove simply because the arsenal didn't bother to change the tooling.
The Luger in the image you posted is a very nice example, but as you can see the transition of the lower part of the chamfer is a bit more apparent than on your rendering, as I attempted to point out.
Your illustration is quite nice. I did not mean to sound critical, I just wanted to help make it a wee bit more authentic. If you are happy with it, that is all that matters.
Best regards,
Ron