I think you may have the RB situation a little mixed up. It should be Rex/Ameer with the others on the rise. Ameer was definitely the top choice after Rex. For some reason people keep putting him farther down on the depth chart than he really was. I wonder if it has anything to do with him being the only 3 star out of the group.
Probably just remembering from early in the year. Abdullah was the KR from day one but it was Green and Heard who were in the backfield quite a bit more early in the season. Later in the year, you saw more of Abdullah back there. As of now, I'd say AA is #2 but he didn't start out that way.