Continuity mistake: When Doug is writing on a board, he holds the board at the end or the top depending on the shot. (00:03:30)
Visible crew/equipment: When Carrie comes back saying she can't swap the flights, there are various tape markers visible on the floor. (00:19:00)
Continuity mistake: The Saskeys are Doug's neighbors in this episode despite them having moved away back in the season 2 episode "Soft Touch" (00:02:30)
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)
Visible crew/equipment: When Doug gets the beach ball, all the stage lights are reflected in it. (00:14:00)
Continuity mistake: When Tim and Doug are talking about the pool overlooking the property, the way Tim holds the ball changes between camera cuts. (00:15:00)
Continuity mistake: When Carrie realises Doug has been in the pool, the magazine in Doug's hand vanishes instantly. (00:18:20)
Continuity mistake: When the beach ball sails over the fence, Doug picks it up and holds it to his face, making his right side of his shirt wet. Throughout that scene, his shirt is dry, and then wet again.
Visible crew/equipment: When Doug and Arthur arrive in the City to talk to Carrie, yellow tape markers are visible on the floor by Doug's feet. (00:15:10)
Visible crew/equipment: We see Doug slide past the camera at Carrie's hospital appointment. When he does, a boom mic is reflected in the picture behind them. (00:11:50)
Visible crew/equipment: Near the beginning when Doug comes into the kitchen and smashes the cake with the watermelon, you can see a stage light reflecting in the door window 3 times as it swings open. (00:00:10)
Revealing mistake: During both opening and closing driving scenes, a light on the back and top of Doug and Carrie's heads slowly flickers on and off but never moves - revealing a stage light simulating driving past street lights. (00:00:20)
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.