Most of what you have read about needed chill hours in pawpaws is simply wrong. There are a lot of myths that have grown up about pawpaws that are simply not fact. There has long been a myth that you can’t grow pawpaws in zone 9 at all no matter how many chill hours you get. I grew pawpaws for almost 30 years in zone 9 in the California Central Valley. In some years we were effectively zone 10. All of my pawpaws leafed out and fruited every single year. During that same time others grew multiple cultivars in SoCal in zone 10 and no one ever had any problems with chilling issues.