The shape of the ground surface is that which you generally see only on factory ground magazine bottoms. If renumbered, the work was very well done, but I fear that things are not right.
Take a close look at the "n" and "u" stamps documented here:
http://lugerforum.com/lugermarkings/suffix.html
and you'll see that the tails of the "n" and "u" are different. The magazines have upside down "n" characters, not "u" characters.
And yes, the other explanation is that the worker that day stamped the magazines with an upside down letter suffix accidentally. Is this a one off that escaped inspection and got approval? Are other examples known?
If someone was boosting them, my bet is that they would not have stamped the letters upside down. Of course, anything is possible.
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.