outfitter
Well-known
Brian
The prewar FED cameras and lenses were matched at the factory. Not only in terms of lens flange to film distances, but parking orientation (the issue you found). Standardisation was almost nil. Two prewar FED cameras will not have the same lens thread start points- interchanging the lenses from either camera to the other would likely result to something similar to your observation.
Jay
Indeed one characteristic for classifying early FEDs was "focusing tab at 11 o'clock", 9 o'clock etc