Really nice looking Luger. The serial number is too low for a 1920 Commercial so the "question marks without a period" almost have to be a letter suffix. It would be great if you could post a clear photo of the frame serial number and marks. I don't think that will explain the lack of any other numbering but it might help, and if nothing else it will satisfy my curiosity about the marks!
I have always maintained that all bets are off on 1920s production guns. They are all over the place on configuration and numbering. They are fairly consistent but odd variations do pop up. As far as value goes I suspect that given the gun is original finish the condition would still place the value up there with the best of the 1920 Commercials. You might have trouble convincing a buyer of that but that is my opinion. The fact that it is a 9mm is also unusual and boosts the value.