Well Corey is in the same shoe as Clayton. He would be maybe the 4th best DB coming in the draft, and probably looks at going early in the 2nd round. If he waits another year, he will be a lock as a medium 1st round pick. That's way too much money to be risking.
Corey was also a partial qualifier, so he has to have enough credit towards a degree to be eligible for another year. They said earlier in the year that he was on pace, so if he kept it up this semester, he should be good to come back.