75595 falls into the serial range of the Swiss Basel canton police pistols (among others), which were produced in 1916 but did not reach the market until after the war's end. Most--but not all--have lazy c/N proofs, and most--but not all--are in 9mm. Any explanation for the observed characteristics is speculative.
This pistol is likely not a Basel police gun. The Basel pistols have a characteristic compressed spot on the right grip, just behind the magazine release, due to pressure from the snap closure of the service holster.
--Dwight
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