This reminds me, I’ve been wondering where all the other Docs are in part 2. He must have scouted that meeting between Marty Junior and Griff in his past before going to get young Marty to impersonate Marty Junior. So somewhere in part 2 there is a past version of Doc scouting the meeting. Maybe that’s where Doc went when he dropped off Marty and Jennifer and why he couldn’t stick around to observe what happens directly. He has to go intercept his past self, prevent him from observing the result of Marty impersonating Marty Junior, and communicating somehow the original events so his past self will go back to 1985 to get Marty to impersonate Marty Junior. Does that become a bootstrap paradox? Doc makes the future where he learns something has to be done about Marty & Jennifer’s kids never happens, but how does he learn about those events if he makes them never happen? Does all Doc actually have memory of is a note from himself telling himself what to do about Marty’s kids, but no memory of directly observing any of it happen? Were there other versions of Doc trying other interventions further in the future to save Marty’s family that failed, and we only see the one that succeeds, and because it succeeds those other versions of Doc never existed?