All film backs are compatible with all bodies. However, the earliest backs (the ones before the Pro-S, including Graflex backs) body do not have the multiple exposure interlock or the the darkslide interlock. The Pro body has no way of preventing multiple exposures–it is entirely up to you to remember to advance the film. Likewise, the darkslide interlock on the Pro-S and Pro-SD bodies prevents you from removing the darkslide while the film back is not mounted as well as preventing you from removing the film back while the darkslide is removed. Both interlocks require mechanical features on the film back as well as the body. This means that you have a Pro-S or Pro-SD body and use an older back, you will miss out on what is probably the most important feature of the new generation–the two interlocks.