Plot hole: Sally Rogers appears on the Stevie Parsons show which is a late night talk show, the next morning she receives letters from as far away as Hawaii... the US mail isn't that fast.
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.
It May Look Like a Walnut! - S2-E20
Character mistake: Rob is having a nightmare, part of which involves the disappearance of his thumbs. When he finds Laura at home, the script calls for him to say, "I want you to help me get my thumbs back," but he actually says, "I want you to help me get my thumb backs." His thumbs are also still there but hidden (you can see a portion of them in one frame of the episode).
Rob Petrie: At least I'll prove one thing tonight: Television writers marry the prettiest girls.
Trivia: During the fourth season, actress Rose Marie suffered the tragic loss of her husband to whom she had been married for 20 years. Amidst her mourning, Marie felt that the grief and pain of loss was too much to bear and wanted to leave the show entirely, just before the fifth and final season. John Rich, one of the show's directors, was there to console her and convince her to come back and finish out the remainder of the show.