Don't quote me on this but I believe machine builders can assign them, sometimes even during setup of the machine. I would think they have a specific one they like to use but it could be a different M code on two of the same machines. It would probably be best to call the machine manufacturer. There does seem to be a lot of post guys reading these threads so they may have your answer off the top of their heads or at least can give you a couple to try. I'll keep checking.
That information is correct. The machine builder / end user can customize the M-codes to their preference. Usually builders will follow Fanuc standards, but it is not always the case. If you can find what Output relay is controlling the air blow you can find it by looking at the ladder of the control.