Of course, but I'm not sure this part:
Originally Posted by
flybywire380
maximum lift coefficient decreases with altitude due to reducing Reynolds number.
(at constant mach) is true to any meaningful degree for a real life situation. There is a dependancy of CLmax on Re, but the difference between say Re 5x10^6 and Re 7x10^6 is pretty minimal.
The useful number from an operational perspective is the buffet margin, and it may well be that small changes due to altitude are neglected so that it fits nicely on a 2D graph (pure speculation!)