In January and February, 1941 the Mauser concealment code was "42" and "byf" which you find on the forward toggle. They were ordered to change their concealment code to "byf" on January 1, 1941 by the Heerswaffenamt.
The reason for the 1941 production of "42" code guns was an overrun of "42" marked forward toggles, almost 16,000.
These appear from the middle of the "n" block through the middle of the no suffix block that followed the "z" block. There are thought to be 15,711 mixed in among 51,697 byf code Lugers in those blocks.
Details are in "the Mauser Parabellum page 225 and 269-70.
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 Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.
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