Well in the first draft of BTTF, George McFly thought of Marty looking like the guy who played at the dance. In that draft there was a picture taken. George looks at it and said something to the effect," can't be." Gale and Zemeckis wrote in the script: it is.
I was talking with a friend about a couple plot holes at the ends of Part 1 and Part 3.
Part 1, where are the Libyans? The whole Fox photo center is gone. Marty runs up to Doc and they aren't in the background where they should be. I would say they got sucked into the wormhole portal, but we know that didn't happen

(could you imagine if they went back to 1955, Otis Peabody would have taken care of those bastards!)
At the house Biff is outside waxing the BMW.
He comes in carrying George's novel. Biff then hands over the keys to the truck. Camera cuts to Marty getting into the garage. Now with film editing, it is possible and intended that Biff left the McFly house because he was all done. There is no Biff truck in the driveway when Jennifer walks up.
So at the end of Part 1 is fair to say that Biff left and that there was a lot of time between when Biff handed him the keys and when he walked out to the garage. However at the beginning of Part 2, Biff is still there and for some reason match books are the big rave
And some how by the end of Part 3, Biff is still at the house, waxing the truck (which has changed a third time).
I love BTTF more than anyone, and you know what, when I first saw BTTF 2, I never thought of it about Biff still being there running out. At the end of Part 3, there was so much shock over the destruction of the DeLorean, I didn't think too much of Biff still being there. It was all just to show the audience that things were normal.
The great thing about BTTF is alternate time lines can explain away most mistakes
