[DonVoigt]

Eugen,
perhaps easier to say what they were Not used for - military production.
Many parts rejected for the military were used by Mauser for commercial production.

I rather doubt this "A" is for reject; but for the odd occurance of the same serial digits occuring in a unit- so one of them was stamped with "A" for quick differentiation.

This practice is noted in one of the books, one of the Police books maybe, but I can't recall exactly where at the moment! CRS strikes again.

This one is a puzzle with the un-numbered parts: another possibility is a post WWII rebuild by one of the Suhl gun makers, with the A added to identify their work; kind of like a trademark seen applied by others- for example Luneschloss.