Really? Do you often fly at FL420 with said crew in the super? Did they not give you an RVSM course with the t/r!
Above FL 410: required vertical spacing is 2000 ft and Flight Levels increase in steps of 20. This means that FL 420 is not available but FL 450 is used instead by aircraft flying in a south-westerly direction. The next flight level for traffic to the north-east is FL 470 and FL 490 instead of flight level 480 to a south-westerly direction etc...
Eastbound magnetic tracks (000º - 179º) at flight levels 450, 490, 530, 570, ....
Westbound magnetic tracks (180º - 359º) at flight levels 430, 470, 510, 550, ...