Assuming you've completed all quests and dungeons in the game and potentially subtracted points based on your choice at the end of the Mages' Guild quest line and the tutorial point if it was a pre-Morrowind character, have you accounted for the skill points from maxing your alliance/pvp rank?
I've just downloaded the add-on to check. It's updated for Greymoor and says the max points available are 455. So if you made your main character before Morrowind, I would say you have all the points that you can.