Gentlemen,

additional information from a collector in Germany:

there existed DWM systems intended for the use in argentino "mausers" which were NEVER proofed and bear no serial numbers whatever. They are therefore still in "mint" condition and have never been assembled.

So I assume that in the manufacturings of large military contracts there have been always some excess systems in spare, which were (if not needed) stored and then the number would have been added the time the rifle was assembled/finished.

best regards
Rolf