Unfortunately, it can be easy, with all the busyness of a film set, for show creators to miss important things. There were actually a number of continuity errors on the show, one of which, was pretty significant.
In one scene, Jack has leaves all over him that appear to change color when the camera cuts back to him. There were some other sloppy mistakes such as items on set disappearing between takes.
There Was Another Roommate Before Jack
Yes, you heard it right, before Jack, Chrissy and Janet had another roommate. Before Jack, their roommate was named Eleanor and she actually made an appearance in the episode, Eleanor’s Return. She was played by Miriam Black.
In the episode, her visit to her former apartment actually had Jack a little nervous he would be replaced.
The Show Had at Least One Famous Fan
Accolades from those already in show business say a lot about the success of a show. Lucille Ball was apparently a big "Three’s Company" fan and even hosted a “best of Three’s Company” show.
Actor Jim Parsons (of "The Big Bang Theory") is also said to be a fan.
The Apartment Address Kept Changing
Observant viewers would have noticed that, during the exterior shots of the apartment, the numbers on the building kept changing. This is because the area where the show was filmed had three different addresses during the show’s duration.
Funnily enough, the apartment complex name (Hacienda Palms) remained the same throughout the entire series.
Jack Lived At a Well-known Location Before He Moved In
Before Jack crashed with Chrissy and Janet, his character’s life story had a bit of a rough patch.
Jack was actually staying at the Y.M.C.A. before he found a new home with the girls at Hacienda Palms.