Well Waffenfabrik Mauser became Mauser Werke A.G. on 30 May, 1922. Obviously, no gun made before that date would have "Mauser Werke" on it because that company didn't exist.
Ezell uses the term "serial number", and I had always thought Mauser numbered those Nickl experimental pistol in their own series. Further, the higher number appears to have the later features. But the numbers may not be serial numbers, or the numbers could be from different series, or even inventory numbers, shop numbers, team numbers, or whatever.