Here's my theory.
I believe it's the same Doc as in Episodes 1 and 2, but somewhat different.
The movies go as planned, however, instead of going back to 1885 at the end (or wherever he decides to go), he and Clara stay and make their part time residence.
At some point, Doc still goes back to 1931 to get the info on Marty's grandma, Trixie/Sylvia, and gets arrested due to the speakeasy fire. We don't know exactly when he goes back though. The DeLorean goes to retrieve Marty in 1986, and Marty goes back to 1931 to rescue Doc. After going back to the future, and seeing the "Tannen Crime Family" timeline, they return to 1931 as in the old timeline. They get Kid Tannen arrested, and return to May 15, 1986. This time, Doc doesn't fade out, and is scheduled to receive the Key to the City later in the day.
At some point when Doc is not with Marty in 1986, Marty most likely fades from existence since he is currently in 1931, trying to break up Emmett and Edna.
Doc in 1986 doesn't realize this until he receives the Key to the City and looks at the newspaper snippet he received in 1931, realizes it's the same Marty from 1986, and returns to 1931 to rescue him.
Now I know lots of people will say, "But wait! How could Doc come from 1986 if Hill Valley was destroyed in a fire in 1876?"
It's because Edna's trip to 1876 doesn't occur until moments after Doc arrives back in 1931.
Therefore in summary, it's the same Doc from Episodes 1 and 2, just somewhat altered lifestyle, having made amends with his father at 17.
I know, it sounds confusing. It's a wonder the space-time hasn't already been destroyed!
Last edited by zelda42293; 07/08/2011 at 10:47 am.