Divination & Arithmancy seem to share the same block all through canon
That seems manifestly unfair to anyone who just wants to take Divination and Arithmancy, not every single elective, and the same goes for anyone else wanting to take the overlapping electives. So, yeah, I fudged a bit. These tables are about equal parts canon and 'WTF, mate? That's not how it should work.'
Same goes for the NEWTs. Not every class can suddenly have fewer students because then...where did the extra students go? They've got to be attending class somewhere.