IMO. If older Doc knew to wesr a bullet proof vest that night, then he must have ed spending week with Marty as young Doc. As far as filling Marty in one what he had been up to since he sent Marty home in 1955, he probably did, but off screen. (Like during the ride home from the mall, during dinner in the blacksmith shop, etc)

I don't think his memories changed. When he mentions the car being wrecked, now his family didn't know what he was talking about. However, I could buy the idea of a slight personality change, even if he isn't aware of his attitude change. But then again, all sequels do a deeper dive into the main character's personality, to help keep their story going, and since Marty was never called a Chicken in the first movie, for all we know, he may have always had that quirk