<p>I'm kind of in a similar boat. Back in the day I used a Yashica 2 1/4" Twin lens for years. I have now, a RB 'Pro S' Body, which is new to me. It came with a 120 roll holder, and 'Pro' back...no markings on it say otherwise and from pics in manual and on web, the "ProS" back is labeled as such. Also there is not a Multi-exposure lever at top next to film advance lever to switch from single to multiple exposure. For my first roll of film I could not advance the film after recocking the shutter. I could cock and shoot over and over, just not advance film. There is, at top center a "film wind stop release lever." I eventually found that if I push that after each shot I can then advance the film... just one added step. Is this due to an incompatibility of the back and the body? If so, can I use my same film roll holder in the ProS back?</p>
Film
wind-stop
release
lever