Revealing mistake: Edward has wonky eyes in some scenes.
Other mistake: The episode's title in the original PBS Broadcast version is "The Old Iron Bridge" but the bridge was made of wood.
Thomas, Percy and the Coal - S2-E1
Revealing mistake: In some shots of Thomas and Percy, both engines have wonky eyes.
Thomas, Percy and the Coal - S2-E1
Revealing mistake: When Toby pulls Annie and Clarabel, the latter coach has a loose roof.
Thomas, Percy and the Coal - S2-E1
Continuity mistake: When Thomas is being covered in coal, he is dirty in some shots, but in other shots he is clean.
Revealing mistake: Each time when Thomas takes a shortcut, the points do not change.
Factual error: When Bertie finds Thomas derailed, Bertie is on the wrong side of the road. The UK drives on the left. Also, Thomas runs under North American directional rules at the beginning and end of the episode.
Character mistake: UK Only: When Thomas comes back to Annie and Clarabel, he calls the latter "Carabel."
Continuity mistake: Gordon's connecting rods change position after he pulls Thomas out of the mine.
Character mistake: Black smoke comes out of Thomas' funnel 50 seconds before the narrator says so. (00:03:40)
Character mistake: In the trivia game on the "On Site With Thomas" DVD, Monty's name is misspelled as "Monte."
Factual error: In the "Steamie or Diesel" game on the "All Aboard with the Steam Team" DVD, Spencer is incorrectly called a diesel even though he is a steamie. Whenever you get the wrong button, Spencer says he actually has a horn instead of a whistle and even says he is a diesel engine.
Thomas and the Billboard - S12-E1
Revealing mistake: At the beginning of the episode, Henry has Gordon's face.
Audio problem: In the US version (Rusty Helps Peter Sam), Peter Sam has a different whistle sound after the trucks hit him. And throughout the episode, a lot of music and sound effects are missing.
Revealing mistake: The old engine's model, who fell off the bridge, was actually Skarloey's, as some red paint can be seen.
Revealing mistake: When the elephant is loaded into the truck, the tracks abruptly end behind Charlie.
Revealing mistake: Peter Sam is already missing his whistle even before it gets knocked off by the branch.
Continuity mistake: When Rusty arrives on the Other Railway, chains are seen hanging beside the signal box, but in the next shot when Rusty asks, "Ooh! What's that?", the chains have disappeared.
Samson at Your Service - S18-E24
Revealing mistake: James is shifted on his body when Samson leaves him.
Visible crew/equipment: When Bill and Ben are shunting, we can see hands. (00:02:00 - 00:10:00)
Answer: Breakdown trains help the engines back on track.