Right at the beginning of the film, they have the Stones in a radio studio, and the leader of the Hell's Angel's, Sonny Barger, phones in and gives a long speech about how they didn't do nuthin' wrong, people were kicking our bikes etc.
The camera then turns to the Stones, and they were asking each other, "Who WAS that guy? Do you remember him?" "I think I MIGHT remember meeting him." The Angels and the Stones met maybe once in advance. You can't really expect the Rolling Stones, who were a bunch of Brits, to know who the hell the Hell's Angels are / were.
Anyway, I had forgotten how how much the film was about the Rolling Stones, probably 90% concert footage and interviews. There were some great informal studio sequences, like where the band sat around and listened to the final cut of "Wild Horses", apparently for the first time. You just don't see film footage like that every day.