I just re-watched the trilogy but I realized something. In Part III, how could Doc be alive to help Marty if he had gotten shot in 1885? Also, was the DeLorean in the cave the whole time Marty and Doc were in 1955 or did it only appear there when Doc went back to 1885? On top of that, if 1955 Doc never invents the time machine, will everything go back to the way it originally was, as seen in the first movie before Marty time travels?