Revealing mistake: The car that goes over the cliff is at least ten years older than the car it's supposed to be - the 1957 Plymouth Fury that Diamond was driving. It's obviously old 1940s stock footage.
Continuity mistake: When Diamond drags the bad guy out of the water, the hunting dog that's been sitting on the dock barking at them disappears between takes.
Revealing mistake: When Diamond and Miss Miller are driving in the country, Diamond is turning the steering wheel in wide arcs as though he's on a winding road. But the rear-screen projection footage behind them is moving in a straight line.
Continuity mistake: While Diamond talks to the newspaper editor, he has two locks of hair falling over his forehead in full shots, but in close-up, his hair is neatly combed back. The forelocks come and go repeatedly after that, throughout the episode. (00:18:00)
The Payoff - S2-E3
Continuity mistake: When he's turning to leave Mr. Wilkins' club, Diamond's hat jumps from his left to his right hand between shots.
Continuity mistake: The 8x10 photo Diamond shows the bartender disappears from the bar between shots.
Continuity mistake: Diamond parks just inches behind an old car and then enters the Chinese restaurant. When he comes out again, the older car is in the same place, but his Plymouth has somehow moved itself back several feet.
Continuity mistake: During the wedding scene at the end, Diamond's hair is falling over his forehead in half the shots and combed straight back the rest of the time.
Continuity mistake: After the wedding, the new bride kisses Diamond good-bye. She's standing just inches from him, but when the camera angle reverses, she has instantly jumped to a spot several feet away.
Revealing mistake: During the fistfight at the end, David Janssen's stunt double's face is visible several times. (00:23:30)
Continuity mistake: Diamond returns to the all-night cafe and parks with his car pointing toward the door. After he goes in and comes back out, the car is in a completely different position, parked parallel. (00:10:20 - 00:11:30)
Visible crew/equipment: When the Highway Patrol car pulls away from the house, the shadows of the film crew (wearing hats), the camera and a light pole are all outlined on its big white doors. (00:16:50)
Plot hole: Diamond is in a very small town in the middle of rural nowhere, and it's the middle of the night. His car has just been wrecked, driven over a cliff by the bad guy. Yet on the same night, in the cafe at the end, he offers George a ride - for that same night - to New York. (00:25:30)
Visible crew/equipment: Diamond parks outside the apartment house, and when he opens the car door, it mirrors several stage lights and reflectors.
Continuity mistake: The apartment manager scares off the street gang attacking Diamond. In full shot, Diamond is leaning over, arms spread across the hood of his car. When it cuts to a tighter two-shot, he's immediately standing straight as he talks to the manager.
Short Haul - S2-E13
Continuity mistake: During the drive to Mr. Neate's house, the cars in the rear-screen projection keep changing instantly, depending on whether the camera is on Diamond, on O'Malley, or on both of them.
Revealing mistake: Diamond's office building has an automated push-button elevator (quite a rarity in the 1950s). But when he and Hastings exit and walk into the hall, the elevator doors remain open long after they should have closed. There's also no break in the floor where the steel plating for the lift car ought to be, making it all the more obvious that it's a studio mock-up rather than a real elevator. (00:01:20)
Continuity mistake: After the bad guys rough up Diamond in his apartment, his hair alternates several times between falling over his forehead and staying neatly combed as the camera angles change.
One Foot in the Grave - S2-E20
Continuity mistake: Two thugs knock Diamond unconscious and leave him in a parking lot. When he wakes up, he's lying in a different spot, farther away from a painted white line, than he was when he fell. (00:05:20)
One Foot in the Grave - S2-E20
Continuity mistake: While Diamond is talking to Yvette, she leans on the record cabinet and one of its doors swings open. A few shots later, though she hasn't touched it again, the door has closed itself. (00:11:15)