But BTTF doesn't show any indication of taking place within an immutable timeline. In fact, the movies go out of their way to show that they take place in anything but an immutable timeline.

Ah, shucks, this is starting to get out of hand ...

TIMELINE-F

PODD

February 20, 2014

DISTINGUISHING CHARACTERISTICS

On this Earth, it is forbidden to discuss the time travel mechanics of Back to the Future in Internet threads that don't explicitly deal with the Back to the Future films. To prevent the accidental reading of such forbidden discussions, technological hats designed to disable the visual parts of the brain upon exposure to such discussions have been invented and surgically grafted onto all persons who have regular Internet access.

FINAL NOTES

Stop talking about time travel in BTTF!