Where There Differences Between The Commercials
 

and military. Workmanship, finish or quality. Here is a 1908 commercial

yes, I can answer not half as smart as most.
Commercials are generally better finished (IMHO) even during war time.
As the 'standard' luger changed, so did the commercial - i.e. 1906 to 1908
Commercials could be ordered in any barrel length - although I am not sure if during the 1920's, if they arrived to America in a 3 7/8" and then longer barrel lengths were added? Or maybe they were mostly refurbished from WW1 from a company like Pacific Arms.
Mostly commercial lugers were essentially the same as military, with I believe a bit extra care. But Commercial to me depends on if there was a war....

This is a 1908 Military~
 

I think many of the the commercials we kept by owners in a closet during the war! The military took the beating~ Check Out The Grips And Military Holster Compared to Commercial above!

As compared to 1900 Test and 1902 Fat Barrel~