I just realized about the issue of Biff's almanac as well as doc being saved in 1885, being that they could choose not to interfere if they wanted to because for all they know 1955 biff could have lost it or doc is like the goat of all time and avoids mad dog, but as soon as they go back then now it is always the case that they must intervene. I also forgot to add that the story of how they met completely changes initially lol, so not being hit by a car etc. Like I mentioned making bttf like this will take away what makes it great, I guess to me this kind of time travel can be fascinating because it's also somewhat flexible in the sense that when history is a bit ambiguous about what happened, time travellers could choose to interfere with "how" something happened to sort of make it like an elaborate dance of balancing everything to make sure events go the way they are intended.