The C means Cab. That part should be obvious... Not sure what they added later on with the 2-speed HST motor or the auto throttle stuff. Maybe that was there from the beginning.
My older M9 is an HDCC3 which denotes Hydraulic Shuttle Cab Creep gears which adds 3 ranges to the gearbox. Note, the 2 speed pto (540 / 1000) has no model letter designation.
Does your tractor have at serial number sticker on dash? My M7040 does and it shows my tractor is a HDC-1 so your model might be listed on sticker if it has one.