Hi Marco, welcome to the Luger Forum! The S/42 is an Ordnance Code used by the Germans to indicate the manufacturer as Mauser. This code was used up to the early 1939 production, then the Mauser code was changed to just "42", then in early 1941 it was changed again to "byf".
Even later, in 1945 it was changed yet again to "svw". Since Mauser stopped Luger production in 1942, the "svw" code is found on their other firearms.
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