Continuity mistake: The buildings seen from the window of Rob's office change in different episodes.
Continuity mistake: The number of glass "pea pod" shaped sphere balls change through out the series. In "Don't Trip Over That Mountain" there were only 3 spheres. In several episodes there were 4 spheres and in others there were 5 of them.
Continuity mistake: Every 4 episodes the table in the living room changes completely, one episode it's a huge oval table, in another it's a medium-sized round table, in another episode it turns into a very small round table, some times it's even a large egg shape.
The Sick Boy and the Sitter - S1-E1
Continuity mistake: The door in the kitchen is wide open in one scene and then the next time Laura and Rob go back into the kitchen the door is closed. (00:07:00 - 00:08:30)
The Sick Boy and the Sitter - S1-E1
Continuity mistake: In the opening scene when Laura answers the phone her hand is on the wall. The shot changes, her hand is now on her shirt.
The Sick Boy and the Sitter - S1-E1
Continuity mistake: Richie's room is completely different from this episode compared to the later episode "The Man from My Uncle."
The Sick Boy and the Sitter - S1-E1
Continuity mistake: In the 1st episode there are about 20 pictures behind the writers desk. Next episode... Gone, replaced with a giant bookshelf and a bunch of scripts. The bookshelf was behind the couch in the 1st episode.
Suggested correction: So they got a new bookshelf between episodes. Or they moved it from another, unseen part of the room.
I fixed it.
The Sick Boy and the Sitter - S1-E1
Continuity mistake: The kitchen walls are completely different than the rest of the episodes. Also, there is no way to look into the living room from the kitchen at the sink. (They fixed that in episode 2 though).
The Sick Boy and the Sitter - S1-E1
Continuity mistake: The whole kitchen is completely different from episode 2 onward till the end of the series. (Episode 2 onward it looks the same except for the outside behind the sliding glass door but the background is also flat. The house(s) and trees are flat, there are also no birds out there making any noise).
The Blonde-Haired Brunette - S1-E2
Continuity mistake: In "Sick boy and the Sitter" the door to the writers room says "Allen Brady Show WRITING STAFF" in a nice 3D all bold caps type font (except for the 1st "N"). In this episode the door then says "Alan Beady Show STAFF WRITERS" also all caps, not bold, and not 3D type font.
Sally and the Lab Technician - S1-E3
Continuity mistake: When Jamie Farr the "Snappy Service" guy comes in and gives everyone their coffee Buddy throws a straw into the straw cup, but it falls down on the floor then vanishes, never to be seen again.
To Tell or Not to Tell - S1-E8
Continuity mistake: In this episode Sally asks Rob if he has a brother, Rob says "Yes, but he is married." However his brother Stacy is trying to become engaged later in the series, in episodes "Stacy Petrie Part 1 and 2."
Continuity mistake: The "Staff Writers" door is backwards. In other episodes the door opens up to the right, not to the left. Also the door is a dark color normally, unlike this scene in this episode where it's a light color. (00:19:41)
Continuity mistake: Rob, Laura, Buddy and Blacky are in Robs basement, there is no wine bar, or giant boulder, and the steps that come down from upstairs lead straight up to nowhere. Because there's a window to the left beside the steps, rather than how it was when they were buying the house where you could see into the house. And there's a giant gap under the wall behind the pool table. There's also a random door that leads somewhere also behind the pool table. (00:24:47)
Continuity mistake: When Laura tries to read the phone number that Rob scratched out, Rob gives her the number as "New Rochelle 69970," which happens to be the Petrie's own phone number, as noted in other episodes.
It May Look Like a Walnut! - S2-E20
Continuity mistake: The episode opens with Rob watching a horror movie on television. The bedside clock shows the time as 9:05. At the end of the episode 23 minutes later, the clock shows 9:10.
Continuity mistake: When Rob is trying to draw the horse and accidentally draws on the wall, the drawing changes depending on the shot.
When a Bowling Pin Talks, Listen - S2-E32
Continuity mistake: Buddy poked the punching bag with Mel's face on it. Then later Mel comes in when the delivery service guy comes. Mel's face is aiming towards the wall. His face on the punching bag keeps appearing and disappearing every time we jump cut from the writers and the delivery guy.
My Husband is the Best One - S3-E14
Continuity mistake: In a different episode the Alan Brady show writers were on a different floor than Alan Brady and Mel Cooley. Yet in this episode they're on the same floor because we can hear Alan yelling at Mell while Rob is in the writers room where Sally and Buddy, currently furious reading the magazine article. (00:14:37)
The Lady and the Tiger and the Lawyer - S3-E16
Continuity mistake: Donna goes back to the den to get her coat to show Arthur. Laura yells at Rob in the kitchen "Rob! Did you lock her in the Bathroom!?" It's a den in most of the episodes... Turns out in this episode it turns into a bathroom with carpet on the floor. (Supposedly when Laura is yelling at Rob in the kitchen).