When Marty reveals to Doc that he is going to be shot by Kid Tannen and his goons, one of the ideas that the player can say is to get Doc a bullet proof vest. Doc denies it when he says "That might work for two or more bullets.". In Back to the Future Part I, in the near ending Doc survives seven bullets from a bullet proof vest.
In some of the Episodes it is said that Doc's interest in science began when he saw Frankenstein (1931). This contradicts in Back to the Future Part III (1990) when Doc's interest in science began when he read Jules Verne's "20,000 Leagues Under the Sea".