Corrected entry: While Rob is by himself at the WOFF radio station the "On the Air" sign is above the door behind him and there is a giant window there beside the door. When Rob is doing the 100 hours of being on the radio the door, the window and room are completely different. No door, record disc holder, other equipment, or window behind him.
Other mistake: Evan from the insurance company comes over to ask Laura and Rob several questions but not once does he find out any names from the party. But the next day Buddy, Sally, Mel, Jerry and Millie all get really angry because of Rob and his interrogator just assuming that they stole the watch.
Suggested correction: Evans says he had all the preliminary information from Rob's earlier phone call including the names of the party guests.
The Great Petrie Fortune - S5-E6
Plot hole: If Rob was just 12 or 13 when he last saw his grandfather (that's what they said in this episode, also he never called his grandfather ever from what it looks like) then his grandfather wouldn't know that he has been working on a TV program. (He started working on the Alan Brady show when he was 20, not before).
Suggested correction: First of all, it is Rob's great-uncle, not his grandfather. And what makes you think he wouldn't know? Off the top of my head, I can think of a dozen ways he could have known. He was watching the show and saw Rob's name in the credits. His brother called him to brag about his grandson. He read a magazine article about television comedy writers. Etc. Etc.
The Great Petrie Fortune - S5-E6
Factual error: Rob tells this lady that the guy that passed away was his great-uncle and that the last time he saw him was when Rob was 12 years old... This is the same Grandpa that was also seen in the episode "What's in a Middle Name" (in this episode in season 5 Richie would be 10 or 11. But the other episode he was supposedly 8).
Suggested correction: You seem to be confused about Hezekiah's relationship to Rob. He is Rob's great-uncle which means he's the brother of Rob's grandfather, the character from "What's in a Middle Name?" (And by the way, the scene in that episode took place before Richie was even born. The fact that they were arguing over his name should have been a clue).
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.
What's in a Middle Name? - S2-E7
Other mistake: Laura tells Sally, Rob and the rest of the staff she's going to have a baby in a few days or so while she was at the Alan Brady Show. If Laura is going to have a baby she should have the baby bump the whole episode while she and Rob are reminiscing. (00:05:00)
Suggested correction: She says no such thing in that scene.
Correction: The studio looks different because when Rob does the 100 hours, he's doing it in a storefront window. People are standing outside and passing by to watch him. He's not in the studio.