I think Greg stops Gerry anywhere from the 5th to 8th round. That's if he's on point with everything. There is an article in SI from 1980 featuring the best young heavys ( with a certain young heavy from Louisville being named #1), and when the story focused on Cooney, Greg gave his opinion on Gerry. And he was on point about how to fight him.
Understand also that Page went from Butch Lewis to Don King around the beginning of 1982, and he was always ranked higher in the WBA than WBC til that time in part because he wasn't a King fighter. There is more to it than is stated.