Have you seen this:
https://en.wikipedia.org/wiki/Contaflex_SLR#Contaflex_lenses
"There was also a Zeiss Pro-Tessar M 1:1 supplementary lens, that kept the focal length of 50mm but allowed 1:1 reproduction. The effective speed of the M 1:1 lens is f/5.6. The 50mm standard front elements, as well as the Pro-Tessar M 1:1 elements, were different between the early models III, IV, Rapid and Super with the old model of Tessar, and the later models Super (new), Super B, Super BC and S with the recomputed Tessar. It appears that the mount was very slightly modified, and it seems physically impossible to mismatch the elements as the journal diameter above the bayonet mount had been reduced by approximately .006""