What's in a Middle Name? - S2-E7
Deliberate mistake: Rob, Sally and Buddy's "old office" is exactly the same shape as Robs basement (except for the door in the center of the back wall. Instead of going upstairs it's all on 1 level. There's a door to the right which goes into a random room which we never get to see inside). (00:10:38)
Suggested correction: Since you listed multiple differences, it's obviously not "exactly the same." Filmmakers not building every set and prop from scratch is not a mistake. Modifying and reusing old sets is just an economic reality of production. If anything this should be under trivia.
The Brave and the Backache - S3-E19
Other mistake: When Rob goes into the office of Dr. Philip Nevins there's smoke rising from the ash tray on his desk. Throughout the scene nobody's smoking.
Three Letters from One Wife - S4-E10
Factual error: Millie mails 14 letters to Alan Brady with names of dead relatives, and to give them different postmarks she says that she drove all over Westchester and southern Connecticut to mail them. The next day, all 14 have arrived. Mail crossing a state line would not likely have made it overnight.
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.
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.
A Man's Teeth Are Not His Own - S2-E13
Factual error: Rob is in the middle of eating a sandwich. You can't break a tooth on a sandwich unless it's frozen, cement, glass or made of ice.
Suggested correction: Rob specifically said he broke the tooth on a chicken bone that was in the sandwich.
The Great Petrie Fortune - S5-E6
Revealing mistake: The great-grandfather Petrie was just Rob Petrie dressed as a really old man. The lamp in the movie is also one that has been in Robs house and Sally's house in a few of the episodes.
