Other mistake: In outside shots the front door is on the extreme right. Shots from inside the house show the living room on the left and the door in a central position.
Other mistake: On the exterior front shots of the house you see the front door with three vertical windows. But on the interior shots it is just one window.
Continuity mistake: In front shots of the house you see that the garage is in the front and opens to the street, but the garage door is behind the house entirely. It seems to open in a back alley or private entrance way. The way it is shown in establishing shots, it can not be open to the front street at the front of the house.
Continuity mistake: In many episodes, scenes are shot on the front porch. It is often shown as a large porch that spans a great deal of the front of the house. But shots of the house exterior from a distance show a small set of stairs with very little space near the door. This isn't a porch on the back of the house as it has been shown to only be door to a small yard.
Visible crew/equipment: Throughout the whole series stage lights can be seen reflecting in the kettle on the Heffernan's stove, as well as on the green dish on a shelf by the kitchen window.
Continuity mistake: Outside shots of Coopers, upper half of each door has 9 windows. 3 sets of 10 windows on either side of doors. Inside Coopers, main doors are all glass and no windows on either side.
Continuity mistake: In episodes that show the outside of the IPS building, there are some shots that show a pay phone outside of the building, then other shots where the pay phone is missing.
Continuity mistake: The Heffernans' house is one of a row of identical brick houses. However from inside the Heffernans' living room, you can see out the side windows that the neighbour's house is beige with horizontal paneling.
Continuity mistake: From outside shots of Coopers, there are no garbage bins or newspaper boxes in front of the pub. From inside shots, several bins can be seen just outside the glass doors.
Continuity mistake: The garage door in the outside view has 4 windows. Switch to the inside scene and it has 3.
Continuity mistake: In the first shot inside Arthur's house, Carrie and Doug are standing together when Carrie mentions how tough it must be for Arthur. It then cuts to Arthur sitting at the table, with Doug right there sitting beside Arthur. Next shot Doug is still standing with Carrie as she urges Doug to spend some time with Arthur, so this is when Doug walks over to his father-in-law. (00:07:00)
Audio problem: While all four guys are on the bed watching the game, Richie's eating a sub so we hear Doug say, "Hey, Richie, come on," but Doug's lips are closed and not moving in this shot. (00:15:10)
Continuity mistake: When Sara is in the shower you can see in her shadow, creases from her swimsuit. (00:16:30)
Answer: Sara hasn't been mentioned in later episodes, and it suggested in later episodes that she never existed, and that Carrie is an only child. Kevin James stated that the producers couldn't think of an good plots to use with Sara, so they left her out.