Since Marty was in Switzerland in alternate 1985 can we assume that he wouldn’t have ended up with Jennifer? Yet, 2015 doesn’t change at all when old Biff comes back. According to Doc, it’s supposed to change around them immediately, because alternate 1985 changed back to normal 1985 around Jennifer, who was there the whole time after they left 2015.
shareYou'd think a plot about time travel would make more sense.
shareI take it you haven’t seen any of the deleted scenes from part two, have you? If you ever get a chance to watch them, there’s a deleted scene where either right before or right after Doc and Marty leave 2015 after they rescue Jennifer to end up in the skewed 1985, the scene shows old Biff where he’s hunkered down behind a parked car and he slowly fades away into thin air so that kind of tells me that if the scene would’ve gone any longer, you probably would’ve saw some kind of a change in 2015 but that’s all the movie showed was up until the point to where old Biff disappeared.
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Changes in BTTF aren't immediate. That's why Marty survived as long as he did in the original BTTF. His older siblings disappeared as their existence became less and less likely. But he lasted until the actual Enchantment Under the Sea dance.
If you MUST apply logic to BTTF, I'd say it comes down to probability. Casino Boss Biff's high living was starting to catch up to him in 2015, which is why he was in so much pain (and eventually disappeared in the deleted scene)
But 2015, Marty's neighborhood (Hilldale) was a slum in 2015. Changing Hill Valley to Hell Valley in 1985 probably didn't affect Hilldale much, so we didn't see anything change.
As for whether Biff's changes caused Marty to not marry Jennifer, that change may have only "caught up" with 2015 after Doc and Marty left the house, so they (and we) didn't see it happen
In the BTTF universe it's like a slow wave....
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