Corrected entry: After Marty burns the sports almanac, it is only burning for a few moments before it begins to pour rain. There was not enough time to burn the whole book, considering he started the fire with some cheap matches and no gas or lighter fluid to make it burn faster. Some of the pages may have survived. There would have been water damage from the rain on the remaining pages for sure, but a few pages may have still survived and have been legible enough for a passerby (or maybe even the western union guy) to be able to read and use to make bets.
Corrected entry: At the end of BTTF, Doc, Marty and Jennifer take off for the future. In BTTF2, they arrive 30 years later and see themselves. Impossible! They would have been inside the time machine (as far as those left behind are concerned) for 30 years. Marty and Jennifer were gone from 1985 to 2015 as far as he and everyone else knows. I can prove this by using the first movie. When Einstein goes into the future one minute, he was gone for a minute as far as Doc and Marty were concerned, even though the trip was instantaneous to Einstein.
Corrected entry: When the "old Biff" steals the time machine in 2015, as Doc and Marty attempt to retrieve Jennifer, it shouldn't be possible for Biff to return to the world that exists around him, as he gets out of the car back in 2015. Doc, Marty, Jennifer, and the world around them ALL should no longer exist, while still trying to escape from 2015. An alternate time line should have been created the moment "old Biff" left 1955. (Thus, Doc's explanation to Marty via the chalkboard explaining an "Alternate Reality"). This all started in 1985, and one result of old Biff's ventures, we learn that Doc is committed to an institution and couldn't even invent, or at least complete, the time machine by October 26th, 1985, which is the starting date of the initial film.
Corrected entry: When Old Biff hands Young Biff the Almanac, the book passes through the film split (the vertical bar that divides the windshield) perfectly because it was on a motorized rig. But the stand-in for Old Biff didn't hold his arm at the right height, so Old Biff's arm disappears into the bar that runs down the middle of the window while the book floats across to Young Biff.
Corrected entry: In the scene where Doc lands the DeLorean in pouring rain in 2015, after a while the rain stops, and it is sunny and you can see the clock tower is in full light when Marty looks at the newspaper. But when Marty, after putting on his new clothes, walks on the street, it is cloudy again.
Corrected entry: When Marty and Doc successfully save Marty's son from going to prison in 2015, the USA Today headline spontaneously changes while Marty holds it. If this is possible, then, when Biff steals the DeLorean to deliver the almanac to his younger self, Marty and Doc's memories would be instantly replaced by those of the alternate 1985 - which would mean that Marty would not be baffled by bars on his windows or locks on his gate when he arrives back home there. In fact, they wouldn't have returned to that house at all.
Corrected entry: How did 2015 Biff know how to operate the time machine well enough to get himself back to see 1955 Biff? He learns about the existence of the time machine from an overheard conversation, which does not include any details of how to set the time circuits nor the requirement to accelerate the car to 88 mph in order to start the time jump.
Corrected entry: Doc puts Jennifer to sleep because she was asking too many questions about her future, and according to him, no-one should know too much about their future. But when they have landed in 2015, Doc doesn't see anything wrong with telling Marty, at length, what is going to happen to Marty in his future.
Corrected entry: In Back to the Future 1 after Marty goes to 1955, you see a sign that says "Hill Valley 2 Miles". Later in the movie, Marty talks to George and Lorraine then walks out the door. The next scene you see Marty with Doc in his 1985 explaining that he needed to change his clothes, and than there is the whole sequence where Marty goes back to 1985. In 1955, in Back to the Future 2, Marty is standing outside the gym when Biff approaches him. Marty is knocked down by his earlier self, and Biff steals the Almanac. Then Marty steals the Almanac, burns it, sees Doc get struck by lightning, receives the telaeraph, runs 2 miles back to Hill Valley, just to meet Doc after his previous self goes back to 1985. How is it possible for on Marty to do the thing previously stated, while the other one dresses and drives to the Clock Tower, taking up the same amount of time?
Corrected entry: The two theories of time travel displayed in the Back to the Future series seem to conflict with each other. In the first movie, Marty changes history to create a future where he was never born, and as a result he begins to fade out of existence. In the second movie, Biff changes history to create a future where Marty is away at boarding school, but rather than fading into his new timeline, Marty stays exactly the same. There are now two Martys, one from 1985 (Marty 1) and one from 1985A (Marty 2). If that's the case, then Marty should have stayed exactly the same in the first movie (Marty 1) and returned to an alternate universe where his other self (Marty 2) was never born.
Corrected entry: When Marty is talking to the Doc when he is in the back of Biff's car, it shows the present Doc with the past Doc's hair (i.e. the actor has the wrong wig on). It cuts back to Marty, then back to the Doc, where he still has the past Doc's hair. When it cuts back to the Doc a third time, he has the present Doc's hairstyle. (01:09:30)
Corrected entry: During the scene where Marty has to duck and move past the car with his other self and Lorraine inside the car, he hears his other self ask Lorraine if she smoked too, in which she replied, "You're beginning to sound just like my mother." Then Marty hears his other self say, "Yeah right.". Problem is, in the first Back To The Future, after Lorraine said that, Marty never said "Yeah right."