Factual error: Krakatoa is west of Java.
Continuity mistake: In the early part when Peter Fonda and Dennis Hopper are getting their choppers ready, the film clip was reversed. You can tell because the American flag on Fonda's jacket has the stars on the right shoulder, not the left like the rest of the movie. (00:06:10)
Factual error: Near the end of the film Butch is complaining about the living conditions they have to endure - jungles, swamps, snakes, night work - and Sundance sarcastically retorts "Bitch, bitch, bitch!" In 1908 the term meant just what it literally means: "Female dog." It did not adopt its current meaning of "complain" until much later. At the time the film is set - outside the context of "female dog" - it was considered to be a serious obscenity, and it would not have been used to describe something as ordinary as someone moaning about his living conditions.
Deliberate mistake: Blofeld doesn't recognize James Bond in this film, even though they met face-to-face in the previous movie, "You Only Live Twice." There is a production-related reason for this. Ian Fleming wrote "On Her Majesty's Secret Service" in 1963 (in which Bond and Blofeld met for the first time), and he wrote "You Only Live Twice" in 1964. However, "You Only Live Twice" was adapted for film first (in 1967), and "On Her Majesty's Secret Service" was adapted afterward (in 1969). Because the 1969 film was so faithful to its source material, Blofeld and Bond are basically meeting for the first time... again. The producers were aware of this continuity problem and intended to have James Bond undergo plastic surgery for "On Her Majesty's Secret Service" (which would conveniently explain Blofeld not recognizing him, as well as the fact that Sean Connery had been replaced by George Lazenby in the lead role). But the plastic surgery idea was discarded in faithfulness to the novel, resulting in a glaring continuity problem between the 1967 and 1969 films.
Revealing mistake: Sam is supposedly far away from civilization, but throughout the movie you can see a ski slope in the background. (00:16:05)
Continuity mistake: At the dinner scene when Mattie Ross is trying to obtain Rooster Cogburn's services, Rooster clears the table, and in the next scene he re-clears the table by pushing everything aside to play cards with Chin Lee.
Continuity mistake: In the scene where the shipwreck survivors are being rescued by Captain Nemo's divers, Nanette Newman is barefoot as she is carried into the submarine. In the shot immediately following, she is being carried into the sub by a diver and she is wearing full length black boots.
Factual error: The Saint picks up a newspaper, and reads an article that is, according to the headline, about the murder of the Englishman he met the previous night. However, if you actually translate the Italian in the body of the article, it is talking about an industrial fire on a ship.
Continuity mistake: During the carriage stroll, the places in the background are not continuous between shots.