Does Back to the Future have a Massive Plot hole? (A Theory)

Zemeckis and Gale created a time travel system that had its own consistent in-universe logic that we the viewer actually know better than the characters. There are several times in the movies where Doc thinks something could be catastrophic but turns out to be fine. Like Jennifer meeting her future self. So back to the future is known by many to have great examples of time travel in storytelling. But does it break its own rules?
in back to the future part 2. Marty and Doc go to the year 2015 to save Marty’s son, Marty Mcfly jr from getting involved with Griff Tannen's gang, effectively putting him in prison. Well during this ordeal Marty buys a sports almanac that holds all the scores to all the sports games from 1950-2000. Marty is like doc cmon and Docs like Nah Marty don't. Well, Old Man Biff sees this and takes the opportunity to steal the time machine and go back to 1955 to give himself the almanac.
Here’s where our problem comes in. When Biff uses the time machine, changes the past, then comes back to 2015… shouldn’t he have gone to an alternate 2015?
So I’ve been thinking a lot about this.

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Видео Does Back to the Future have a Massive Plot hole? (A Theory) канала joey wehnert