Other mistake: On the death certificate for Chrissie, the shark's first victim, the date of death is July 1st. But later, on the reward paper posted by the boy's mother, it says that the date of Alex's death was June 29th. Alex died after Chrissie, not before. Also, the form refers to the coroner as the "corner," and Jun 29th 1974 was a Saturday, not Sunday. (00:09:05 - 00:18:10)
Other mistake: There's a horse that has apparently ridden up a cliff, and an electrical burning brand that can be changed onto different flame settings.
Other mistake: It's revealed that the Knights who say Ni can't say "it" (at least, after they become the Knights Who Say... that other thing), but they still say "it," most notably when they're telling Arthur to place the second shrubbery next to the first one - "When you have found another shrubbery, you must place IT here, beside this shrubbery..."
Other mistake: Clay Tanner plays Jack Henderson in this film, yet the end credits list him as "Delbert".