Here's one thing we probably don't think about too often - but I think it would be very likely for LP Marty to have some scars that TP Marty doesn't have, and vice versa. I know the much debated topics are if Marty will retain his memories of the TP timeline, and also if he will ever regain his memories of the LP timeline. I think one thing many don't take into consideration is the physical appearances of TP Marty and LP Marty. At what point do you suppose the scars would shift on Marty's body? Would it be right after returning to 1985, or sometime before then?

If you need a more obvious example, let's use one that Blind Spot once suggested. Say that George or Lorraine was to go back to 1955 with Marty, and Marty found a way to knock George or Lorraine out for a week - and then the events of that week go the same way as what happened in the movie. The only difference is that George or Lorraine is knocked out in Doc's lab. At what point would George or Lorraine start to physically alter? Would it be as soon as their younger selves kiss on the dance floor, or not until after they return to the year 1985?

Someone else also suggested Marty bringing Doc's corpse back to 1955. At what point would Doc come back to life, and do you think he might remember things about his afterlife?

BTW, it's scenarios like this that further cements my belief that Marty would eventually gain two sets of memories, shortly after returning to 1985. I even recently wrote a story where Marty Jr steals Doc's time machine from 2015 and goes back to 1985. After Marty Jr managed to prevent his father from racing Needles, Marty Sr's life would suddenly improve - and Marty Jr would most likely end up becoming a more confident person in the new timeline.

I think the physical scars happen once the time is altered.

So, for example, say that Marty brought George or Lorraine to 1955 - George or Lorraine would probably transform as soon as their younger selves kiss on the dance floor? Theoretically, this sounds easy enough. However, what if it was Doc's corpse that Marty brought back to 1955? Would he just come to life, as soon as Marty manages to warn Doc of how he gets killed - which would probably happen much sooner? If so, what would he remember, as soon as he came back to life?

As for the memories, someone did once suggest that Marty may have already had his new memories by the time his mother reminded him that he was planning a trip to the lake with Jennifer - but that he was just incredibly confused. After all, he never did talk to his mother in the old timeline about going to the lake with Jennifer - as he knew that she would disapprove.

That was the same time he said that he couldn't go because of the car.

Right! I think his memories did come to him fully by the time Griff called him a "chicken" in the Cafe '80s.