Continuity mistake: In an episode fairly late in the life of the show, Lou Grant says that when Mary came to interview for a job at the station, she bumped into the desk in his office and said, "Excuse me" to the inanimate object. However, we saw that interview in the very first episode, and no such thing happened.
Continuity mistake: In the first episode, Mary gets the job as associate producer. Later in the series, Lou tells Mary that she got the job due to the awkward way she tried to cover a run in her nylon. At the job interview, Mary isn't even wearing pantyhose, she is wearing knee socks. You do not see her trying to cover up a run in her socks.
Continuity mistake: This episode and scene has been referenced already but contains another error. In the scene where Lou is recalling the first time he met Mary, he claims Mary had asked for a job as an assistant producer when in fact he gave her the job because it paid less than the secretary job she wanted.
Factual error: In this episode, when the show opens, it shows the outside of a restaurant where the news team meets for lunch. If you look closely, there are palm trees on the left side of the screen next to the restaurant, almost hard to see because the tops blend into the roof of the restaurant. Everyone knows that because of its climate, Minneapolis does not have palm trees. Perhaps even more noticeable is the huge hotel looming above the restaurant that says "Sheraton Universal", a well known hotel attached to Universal Studios in Los Angeles.
Other mistake: In this episode, the news team is asked to go to the office of the head of the station. Before the scene, the camera pans up the building to one of the top floors. In the scene, you can see shorter buildings outside the office including a dome on top of a building that could be a church or a government building, which would never be that tall. The biggest mistake is that you can see trees right outside the building. There are no trees that would ever be that tall either.