If I look at a profile that has been granted permission to all the Apex Classes listed for my org then the total number of classes allocated is 750. If however I go to the same page on a permission set the total number of classes listed to which I can grant permission is over 2000. I am interested in why the difference?
I have seen some comments that the class list for the profile may only show package classes that are marked a global. That makes some sense but in which case why is the filtering of classes for a permission set not using the same logic.