Any Mamiya lens shutter can be cocked manually, on or off the camera. In fact, C220's and earlier "C3's" (IIRC) don't cock the shutter when the film is advanced, it has to be done separately.

On my C220, I can cock the shutter (without advancing the film), but I still have to move the "button" to multiple to fire. It's probably very similar on your camera.