Big Dougie - S2-E21
Revealing mistake: When Doug is jogging in the marathon he is casting three shadows in different directions. Also, the female jogger behind him appears to be in good shape but is still jogging as dramatically slow as Doug. (00:19:20)
Revealing mistake: When the lights go out at the end of the episode, there is a reflection from a stage light very visible. (00:20:30)
Queasy Rider - S2-E1
Revealing mistake: Doug falls off the bike at one point and shouts that he has had enough. He opens the door and if you look carefully a stage light and boom mic are reflected in the glass. Slo-mo may help but is not essential for spotting the mistake. (00:15:25)
Window Pain - S5-E2
Revealing mistake: When Arthur jumps over the turnstile at the subway where Spence works you can see it is a stuntman wearing the same outfit as Arthur. (00:37:15)
Queasy Rider - S2-E1
Revealing mistake: When Doug is seen giving a lift to Arthur, and Arthur is holding on very tight, the background is so very projected. (00:13:05)
Revealing mistake: While Doug and Carrie are heading home after game night at the Palmers, they pass the street sign for Buena Vista St, twice, as they're driving up Magnolia Blvd in Burbank, CA.
Revealing mistake: When Carrie holds the paper towels, the kitchen's curtains over the sink are normal, the window is closed and the blinds are down. However, next shot the blinds are up, the double-hung window is oddly open outward sideways, and the curtain is pulled back with a large clamp. Then it's all back to the normal previous way.
Revealing mistake: While Doug is driving the IPS truck he stops in traffic, and then Arthur pulls up alongside. Watch the reflection in the truck's side mirror, because we can see crew members pushing Arthur's car as he takes off. (00:19:10)
Train Wreck - S1-E20
Revealing mistake: Shari from ISP radios Doug about the rush order pickup at 1202 Stratford, so Doug pulls over and soon Carrie pulls him to the back of the truck. Cut to exterior shot of the truck, and the street sign reads "Lafayette, Culver City" which reveals the California location. The truck is parked on Culver Blvd, corner of Lafayette, in front of the well known Washington Building (awnings are now black), which is located a few blocks up from Sony Pictures Studios where King of Queens was filmed. (00:21:35)
Revealing mistake: After Doug successfully trades vacation days with Roger, it cuts to Doug's IPS truck stopping in traffic. The next few shots were filmed on the streets at Sony Pictures Studios lot. In the shot of the IPS truck's side-view mirror (as the RV approaches), note the signs on the building read "Keaton Building" and "Sound Department Courtyard." After the flashback, another building sign reads "Durante Building." These buildings are located at the north side of the studio in Culver City, CA. (00:03:20)
Revealing mistake: At the start, when Arthur returns the book to Carrie then asks if she'd like to jot down his musings, we can see through the back door's window, and the backyard set's foliage pattern wallpaper is falling off the backdrop. It's visible later as well. (00:02:45)
Strike One - S3-E5
Revealing mistake: In the kitchen, when Doug tells Carrie he knows the strike will end in 1 or 2 weeks tops because he's a Union Member, the blue shelves/cabinet on the wall behind Doug are positioned properly. Then, when Carrie asks him what the strike issues are, watch as the blue shelves move sideways behind Doug (this wall with blue shelves/cabinet is hinged to provide camera access). (00:13:00)
Court Date - S1-E17
Revealing mistake: When Carrie kicks Doug Spence and Ritchie out the bedroom she shuts the door and the set wall wobbles very noticeably. (00:07:30)
Revealing mistake: When Carrie leans on the fence to hide from the Saskeys, the fence moves. Fair enough Carrie is not a professional carpenter and has put the fence up in an afternoon. However, Tim, explains that the fence is not likely to fall due to how well Carrie has built it. (00:06:00)
Hungry Man - S1-E21
Revealing mistake: When Deacon drops the suit off to Doug, Doug parks the truck up and Deacon gets in, however the outside of the truck is still moving as if Doug is driving. (00:07:50)
Hungry Man - S1-E21
Revealing mistake: When Arthur plugs the blender in you can see the wall move. (00:02:25)
Revealing mistake: When driving the Mini, the reflection on the bonnet never changes despite being on the highway. (00:12:00)
Revealing mistake: As Carrie skids into the parking spot at the start, skid marks are visible on the floor from previous takes. (00:00:30)
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.