Well Back to the Future ISN'T a bootstrap paradox as the events originally played out differently.
That's my point, though. Without Marty's involvement in the events of 1955, the Marty of 1985 couldn't have existed, because the original 1955 without his involvement couldn't have produced him because Biff was originally infatuated with Lorraine and the pre-time-travel George wouldn't have stood up to him to keep him from taking Lorraine.
That is,
unless there was a whole series of events in the original timeline to explain it. My immediate thought was that maybe Biff was drafted and would have had to leave Hill Valley for military service, whereupon Lorraine would've gone back to George -- except the Korean War was over by then, so no, that wouldn't have done it.
I think George being able stand up to Biff not being a one-off thing is shown well enough by the final scene in the altered 1985 where Biff is waxing his car.
Except that's the post-time-travel Biff and George dynamic. The pre-intervention 1985 is consistent with the pre-intervention 1955, which should have led to Lorraine ending up with Biff, since Biff wanted her and the pre-intervention George couldn't have prevented that. Something would have to have altered his character in such a way that he
would have stopped Biff -- but that something was the series of events Marty put into motion --
or a series of events similar to them in their effect on George's character.
Now here's a real wanger for ya -- What if Back To The Future has an unexplored tie-in with Quantum Leap? That would explain why original George was able to marry Lorraine but then eventually regress to his 1955 wimp character. The George that originally married Lorraine was actually Sam Beckett.
Nope, Lorraine ended up with George in the original timeline without Marty. As you say it started as Florence Nightengale Syndrome and they were still together thirty years later, albeit in an unhappy marriage where George was always a bit of a loser and Lorraine was fat and such. Marty travelling back in time almost ruined that because he pushed George out of the way of the car, but they ended up together and stronger than originally after George punced out Biff. So Chuck Berry wrote the song originally in the "unhappy marrige" timeline and that's how Marty knew of it.
That last observation doesn't quite work. Okay, imagine you're Check Berry. You get a phone call and hear 'Johnny B. Goode' over the phone, or a fragment of it in very low audio quality.
There are two possibilities -- one is the Boostrap, but the other is the opposite of a Boostrap:
1. You hear that song fragment and figure, 'What the hell, it's some punk whose gig is a high school dance, I can flesh out my own version and record it.' So you do. And your own version of the song you heard... is still the song you just heard. You got the idea for your song from hearing your song. Bootstrap.
2. You've already been working on the song on your own -- but then you hear somebody else playing something incredibly similar. You don't want to be accused of ripping off the other guy's work, so you drop it. You never finish. The song never exists. The kid who came back from the future doesn't play it because he never heard of it. Anti-boostrap.
Lorraine only ended up with Biff in the dark 1985 of part 2 because of old Biff giving his younger self the sports book and Biff having George murdered.
That's how he got her in that timeline, sure -- but his original, pre-intervention 1955 self didn't have to go to those lengths. And there's no reason why he wouldn't have except for George laying him out -- which only happened because of Marty's intervention in the timeline. Remember that Marty and his siblings kept fading out of that photo, but that wasn't exclusively because he got in the way of his parents meeting -- it also happened because of George's personality -- the same personality George displayed in the original 1985. Marty's non-existence was never a risk of Marty's behavior, but a risk that arose from his own father's unaltered personality. That last sentence is the crucial point. Without Marty's catalyzing George's personality change, Marty would never have come to exist.
