One possibility to distinguish between our different Fritz Neumann’s is to compare the signature. The following list shows examples of Fritz Neumanns signatures, the source images are linked in the image caption:
Signature our Fritz Neumann, taken from this post
© Ric - An unknown artist MMXXI
This work is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, where not otherwise stated.
Ric - An unknown artist is a Projektemacher blog