Interesting. I actually have 4 50mm f1.8 Zuiko's.. An early chrome-nose serial 250000, a slightly later black-nose serial number 800000, a later MC serial 1 mil, and a 'made in japan' serial 3 million.
The #2 with the serial 800000 does not have the notches. I cannot move the ring either.
The other 3 do have notches. #3 and 4 are slightly longer than the others.
I do have the exploded parts diagrams, and they all appear to work the same. Although the later versions, MC and NMC, have a one-peice ring wheras the earlier versions have 2 peices. The outer name plate ring and the inner "stepper cone' or whatever you may want to call it.
So maybe you need to add a few drops if solvent to the threads and wait for a few minutes. then try it.
Sorry I couldnt be more help.
