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: 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.
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: 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)
Revealing mistake: During the fistfight at the end, David Janssen's stunt double's face is visible several times. (00:23:30)
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.
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.
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)
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.
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.
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.
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)
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.
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)
Continuity mistake: The 8x10 photo Diamond shows the bartender disappears from the bar between shots.
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)
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)
One Foot in the Grave - S2-E20
Continuity mistake: Diamond's hat falls off during the fight, then moves itself to a different place on the floor between takes. (00:22:15)
Snow Queen - S2-E21
Continuity mistake: Diamond's loose tie tightens itself between shots when the doorbell rings and he crosses the room to open the door. When he picks up the phone, the tie is loose again, but when he opens the door to leave, it's tightened. (00:42:15 - 00:45:00)