The "Other" Marty.

People always bring up that when Marty returns to 1985, he is now living with a family he doesn't really know.

But what about THEIR Marty? We assume that it's Marty's past self he witnesses escape from terrorists while standing next to Lone Pine.

But.... I have to conclude that it's really not him. This is "Cool George & Lorraine's" Marty. This is the one that grew up in a successful household and owns a 4x4 that Biff shines.
"When" did he go? We automatically assume we're just watching him accidentally go back to 1955 to start the process over again.
But I conclude this can't be. If that were true, this Marty would be going to a 1955 that already contains a mysterious kid people call "Calvin" who is seemingly interfering with his parent's lives. In this Martys reality, "Calvin" has already been present to put his two cents into the events of 1955. When Marty actually does returns to 1955 to fetch the almanac, we see that it's only the orginal Marty present and the events are playing out the way we have already seen.
Thus I must conclude that 1985 Doc (who is now armed with some key information about that night) may have purposefully input a different date into the time circuits in his tutorial to Marty.

Now that would make an interesting side adventure story. When did "sucessful" Marty go? What did he do? How does he get back?