The trigger plate looks like it's had different wear than the nearby receiver.
1937 was a year of transition, and included both strawed and salt blued trigger and safety lever parts. Likewise, some pistols were salt blued, and others rust blued.
What bothers me more is the contour and profile of the safety lever, which appears to have been ground down and re-numbered.
Here (by reference to the ad) is the lever on the pistol that is for sale:
Here's one of my Mauser Lugers (below)... You can see (above) where the top layer of the lever has been removed toward the end on the for sale Luger...
Marc
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Igitur si vis pacem, para bellum -
- Therefore if you want peace, prepare for war.