The Night of Miguelito's Revenge - S4-E12
Character mistake: The store window's sign says, "Denver Mercatile" rather than "Mercantile."
The Wild Wild West (1965)
1 character mistake in season 4 - chronological order
Starring: Robert Conrad, Dick Cangey, Ross Martin, Whitey Hughes
The Night of the Avaricious Actuary - S4-E11
Continuity mistake: The letter from the Cyclops Insurance Company that Gordon pulls out of his pocket is folded, wrinkled, and well-worn. In the close up of the same letter West reads, the letter is white, pristine, and not wrinkled or folded.
Trivia: Due to the rigorous stunts he performed, actor Robert Conrad would often rip out the seat of his already too tight pants.