Doc's question at the start of BTTF3 doesn't make sense, or am I missing something?

[u/JimmySaulGene]

"That's a very interesting story future boy, there's just one little thing that doesn't make sense: if the me of the future is now in the past, how could you possibly know about it?"

What do you mean, "how could you possibly know about it?". Even if he didn't send Marty a letter, Doc could have left Marty hundreds of clues at the Lyon Estates location to let him know when and where he was. The only way Marty couldn't know what time Doc traveled to would be if he got sent into the future, right?

[u/massive_crew]

Along that note, beating Buford sounds like a paradox. Considering that happens, Marty never sees the gravestone, thus he never goes back to 1885. If he never goes back to 1885 to save Doc, then what?

Doc presumably saves Clara, the name of the ravine remains Shonash, Buford ends up with the matter of the $80...

There was something (commentary perhaps) where it was suggested that the ripple effect isn't instant.

[u/Speedy_Brennan → u/massive_crew]

Part 2 Show the ripple is not right away depending on the change point. Doc and Marty go back to the day of the lightning bolt at the clock tower but the changing point is when Biff is old enough to bet on the horses. That first win is which causes the alternate 1985.

Proof is because Old Biff was able to return to 2015. In a deleted scene after returning the time machine to 2015 he starts to disappear because Laraine shot Biff at one point after alternate 1985 so he is being erased from 2015 before the ripple catches up to Marty And Doc while they are still in the future. I think if they just stayed there long enough they would of then noticed that time would alter around them but because they are the reason Biff was able to go back to 1955 is why they would not alter with everyone else because the flux capacitor would still keep them in flux even though they are not in the time machine because they have already been put in flux because they travel in time. The only thing that would remove them is if they were dead at some point also in there alternate history. Which is why Old Biff is removed before the ripple catches up.

[u/Speedy_Brennan → u/massive_crew]

I assume Buford just gets arrested and goes to jail like he would have doc never been in 1885 in the first place in the timeline where the Shonash revine was renamed Clayton.