That is all I have to say about that.

Not!

Seriously folks, Marty Prime is ending variations of everybody all the time.

What happened to the loser versions of his parents and siblings? Gone! What about 1985 jerkwad Biff? Gone. The 2015 version of pretty much all of his friends/family- gone. Bifftastic 1985? All gone.

And to Ryan's question, I don't think 1885 Doc has any memories of what 1955 BTTF3 Doc did- or else he wouldn't be surprised to see Marty show up in 1885. Unless, as is somewhat suggested by the films, these things can take some time to propagate throughout space-time. Perhaps by the end of BTTF3, 1885 Doc does remember sending Marty back in time to 1885 from 1955.

Regardless of whether you're a time traveler or not, there is an official timeline and that official timeline includes 1955 Doc sending Marty to 1885.

However, the official 1985 now has awesome McFlys, but does Marty ever remember any of that? Again, he is surprised to see awesome McFlys upon his return to 1985... but do those memories fill in a week later? Memories of things he didn't experience, but should? Or did those memories go back to 1955 with "Awesome" Marty McFly at the end of BTTF1?

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Back to ending variations of these people, it's really no different from cause and effect in our linear existence. We all end possible versions of people by interacting with them. We just never get to see what could have been if our actions were different, and Marty does.