re: BTTF time travel quesiton / Johnny B Goode

Obviously it creates a bit of a paradox, but the idea is that Marty gives Chuck the idea of the song thanks to Marvin making the phone call.

It was supposed to be a little chuckle in the movie, but if you overanalyze it too much, it doesn't make much sense.

Just like George and Lorraine don't recognize Marty as literally the same guy they knew back in high school, or anybody else at the school not recognizing that Johnny B. Goode was played at their HS dance long before Chuck berry made it famous.