Yeah M4AC is for the M-400A2 FCO, M4RC is the M-400R2 FCO, M4AR is the drop lens M-400A2, M2AC is the M-250A2 FCO, the M2RC if the M-250R2 FCO, M2AR is the M-250A2, and the M2RR is the M-250R2 for ordering numbers.
I hate it when the lights are called by their ordering number instead of the catalog number lol. I wonder if the seller is a member of here or the GoL or at least a light collector?