Graflex roll holders have autostop. If loaded properly, the holder will stop advancing film when frame one is ready to be exposed, and after that will stop when the film has been advanced one frame plus the interframe gap. Autostop will work until the film is advanced to the last frame (8, 10, 12, depending on whether the roll holder is designed for nominal 6x9, 6x7, or 6x6). After that autostop disengages and its up to you to advance the film one frame plus the interframe gap. I suppose you can work it out, but if you don't get it right, the length of film in the gate ready to expose after you've gone past the last frame will be somewhat random. You may also have film flatness problems because the end of the film, if in the gate, may buckle a little.
If your RB Super D has a Graflok back, you can use (if you can find one) an Adapt-A-Roll 620 roll holder to get 9 frames. These devices don't have autostop, will give 9 nominal 6x9 frames/roll if loaded correctly.