Corrected entry: Doc is always banging on about making as little impact as possible in his new life as an inhabitant of 1885, yet the method of exit he chooses will change hundreds of lives and cause huge disruptions to all sorts of timelines. The train they destroy would not have been easy to replace, and would have been used by hundreds, maybe thousands of travelers to get to places they are now not going to get to, to meet people they are now not going to meet, to start family lines that now don't exist, and so on on so on. Now that Buford is no longer a threat, a far better alternative would be for Marty and Doc to leave town and live quiet, anonymous lives somewhere isolated - something Doc has already thought of and a far better idea than their returning to the future in such a damaging manner.
Corrected entry: At the onset of the film, Doc and Marty discover Doc's grave from 1885 with the dedication by Clara Clayton on it. Now remember, this was before Marty had gone back to 1885 to meet Doc and further influence the happenings in that year, which included their chance meeting with Clara when she almost died. Even without Marty's influence in 1885, history of the film series up to that point said Clara went over the cliff and died. So therefore, it is inconceiveable that Clara could have lived to even meet Doc to put the dedication on his grave, as he died a few days after she would have.
Corrected entry: When Marty is sent to 1885, he arrives at September 2nd, 1885. Then, Doc has to meet Clara at the station the next day, September 3rd. But when Doc and Marty are figuring out a way to reach 88 miles an hour with the DeLorean, the calendar shows "September 4th" and they still haven't met Clara.
Corrected entry: When Clara and Doc are hanging off the train barely, Marty lets the hoverboard go so Doc can save himself and Clara, which he does. When he pulls away from the train, the camera is shooting from Marty's P.O.V. and it shows Doc pulling ahead of the train and past the Delorean. He would slow down if anything, not speed up, especially holding Clara.
Corrected entry: When Doc and Marty are in the old mine looking for the Time Machine they bust open the sealed entry and find it. The entry is too small to get the Time Machine out. Even if we assume that they made the entry larger, how did the 1885 version of Doc get the Time Machine into the room through the smaller entry back in 1885?
Corrected entry: How come the Native Americans aren't surprised at all when a racing Delorian appears from thin air in front of them, in dazzling futuristic lights?
Corrected entry: At the beginning of the movie in 1955, Marty has Einstein with him and left him with Doc of 1955. At the end of the movie Doc from 1885 went back to 1985 to see Marty and said he had to come back for Einstein, but wasn't Einstein with the Doc of 1955. So how did Doc get him back, is there some kind of explanation?
Corrected entry: As the train approaches the DeLorean there is no wooden scaffold to hold the rubber tyres acting as a buffer, yet in the next shot a few seconds later, there is a wooden scaffold on the cow catcher.
Corrected entry: The arrow stuck in the side of the DeLorean is perpendicular to the car, but that side wasn't facing the Indians during the chase so they couldn't have hit it.
Corrected entry: Given that Doc is so concerned about influencing future events, why does he set up shop right in the middle of town (creating a lot of loud and noisy inventions) and attend town meetings, and volunteer to pick Clara up at the train station? He should be a hermit, living as far away from people and civilization as possible.
Corrected entry: When the 1955 Doc Brown and Marty went to retrieve the DeLorean from the cave, the passage between the room containing the car and the rest of the mine was rather narrow, and to remove the support beam on either side of the opening to widen the opening is to risk a cave in. How did the car get in there or out? Piece by piece?
Corrected entry: When the DeLorean travels forward through time at the beginning of the first movie, the car gets covered in ice. During all other subsequent time travel, this does not happen.