Plot hole: In the episode "That's my Boy" when they bring Richie home from the hospital, Rob and Laura are living in the new house they have. However, in the episode "Where did I come from" when Laura went in to labor, they lived in a different house. They couldn't have moved while Laura was in the hospital.
Other mistake: Mainly in "Who Stole My Watch?" and 2 other episodes the the Petries and the Helpers talk about the Helpers dog, but there is no dog, the dog doesn't have a name they keep saying "our dog" or "their dog", and there's no dog house, water bowl or food bowls for a dog at their house in any episode.
Other mistake: Any time Rob has to go to a doctor or to Jerry to get his teeth worked on, if you look at the window behind him and whoever is working on him. It's the same buildings every time. Even though he goes to different doctors. Also, that window and the curtains are also the same exact windows and curtains in Robs office.
Factual error: Rob mentions several times "I broke my cheek" if he actually broke his cheek we could see a spot there, either a divot in his face where the accident happened and was not fixed, or we would see a indent line from where they put stitches on his face. We see neither of these.