Maybe it's just the result of letting a bp grow out naturally in an open environment over many years? I don't think there are that many 15 year old captive hatched normals in the trade. Maybe after many years of growing, some of which without laying eggs, ball pythons just get to the '6-7 feet' that all the wildlife fact descriptions say they can and all the hobbyists say they can't based on their own anecdotal evidence?