Throughout the trilogy, the DeLorean and its duplicates created via time travel make fifteen trips through time, thirteen on-screen. Seventy years into it, for a few hours, there are four instances of the car. Still not convinced? Consider the one hundred-year gap near the end of this movie, when Marty takes the DeLorean on its final journey. If we grant that all three of those instances (1-3) continue to exist in the "final" timeline, then there should be no problem accepting this theory. Once the DeLorean is in 1885, consider what it would detect (if it were in a position to witness the comings and goings of its former selves): over seventy years of peace, then (1) arrives, then (2) and (3) arrive in some order (2) then leaves at 6:38 p.m., (3) leaves around 10 p.m., and (1) leaves at 10:04 p.m. It is *entirely true* that *we* do not ever witness a moment in the films where all four instances coexist, but the text "ordered from its point of view" above should hint at a solution. Those who do not agree with (4) argue that according to the "ripple effect" timeline as presented in the films, there wouldn't be a DeLorean hidden by Doc in the mine until later that evening, when the lightning blast would accidentally send Doc back to 1885, thereby altering the timeline. (4) The instance when it was waiting in the abandoned mine. (3) The instance when Marty and Doc came back to 1955 to take the almanac back. (2) The instance when Biff came to 1955 to give himself the almanac.
(the time he left), there were four DeLoreans present in Hill Valley (ordered from its point of view): (1) The instance when Marty was trapped in 1955 in the original movie. On November 12, 1955, between the time Biff arrived (or 6 a.m., whichever came later) and 6:38 p.m. There are two theories, one of which drops the last item. Another interesting conclusion is a point of contention. By the time Marty made his ultimate return to 1985, he was approximately fourteen days, three hours, and twenty-seven minutes older than he should have been Jennifer, on the other hand, is seven hours and twenty-six minutes younger than she should have been. There are a few interesting things to note: Not counting the time Doc traveled by himself, the DeLorean spent nearly seventy-one years (on its own time scale) from its first time travel to its destruction. There exists enough clues in all three movies to reconstruct the travels of the DeLorean precisely (to within a few minutes at worst, except 2015 Biff's arrival in 1955 and Doc's personal travels).