I'm pretty sure in the last game or the game before against the Clippers, they said Cory has really been working on his finishing. I can't remember the exact quote as I was upset with the game, but they said something along the lines of finishing in the NBA is very, very hard and Cory's been working on it with the coaching staff a lot this season.
It may have been a strength of his before the NBA (if that's what you're saying), but he hasn't really been consistently good at it until this season in the NBA.