question about aeons abilities

Ok, so I'm learning abilities for my aeons, and all of a sudden I notice the list altered itself when I taught an aeon an ability. I think a different ability I didn't teach it yet disappeared. Does the list eventually expand itself for each aeon, and if abilities disappear, how do you get them to come back? I was trying to get them to learn every ability.

Some abilities require the use of the same items. when you learned your first ability, you ran out of the item for that ability. Since the second ability needs that item as well, it does not show on the list. When you get more og the required item, the ability will reappear.