Sadly, BBL has not documented the custom gcode they use.
I have been working to decipher what I can and create a list, but I don’t have the information for 620.
M621 and M622 seem to be used to do runtime condition checking for some things, instead of macros that expand in the slicer. For example when you disable the calibration in the print dialog.
M620 appears in the P1P startup code looking like a conditional based on the AMS. However, it could be used for anything given the variations such as M620.1.
I am going to add a poll for getting gcode documented and see if we can push enough to get BBL to listen.