Visible crew/equipment: During the drag race at the end, several times on the van you can see camera shadows. (00:19:10)
Character mistake: The woman in the store claims that the umlaut on the shoe size indicates a half size in Europe. This is wrong because the European shoe size system (used in Germany among others) is completely different from the US system. Carrie's 6 1/2 shoes would be a size 39 according to the European system.
Continuity mistake: When Doug and Carrie are arguing over Arthur having a house, the head on Doug's beer keeps changing size. (00:02:00)
Revealing mistake: Both times when you see an overview of the bridge, it's the same clip being used. (00:07:10)
Visible crew/equipment: The second time Doug pulls up at the toll booth, stage lights and equipment are reflected in the car's paintwork. (00:07:20)
Dog Shelter - S5-E23
Visible crew/equipment: When Doug finds out that Rocky is in fact Rocky 4, a boom mic is reflected in the window. (00:10:20)
Dog Shelter - S5-E23
Factual error: Rocky the dog, who turns out to be Rocky IV, is a mixed breed. It would have been impossible for Doug's parents to find three more adult dogs who looked near identical.
Taste Buds - S5-E24
Other mistake: When Doug sits down to eat and Arthur touches his food, Doug says, "That's what my sandwich was missing, a finger with a loose bandaid on it," and pushes Arthur's hand away. When he does this you can see Arthur isn't wearing any bandaids on his hands. (00:00:05 - 00:01:00)
Taste Buds - S5-E24
Continuity mistake: Just after Carrie tells Doug that she knows what he has been doing, she storms out of the kitchen. Doug has his hand on a water bottle on the table, then picks it up as he rushes after Carrie. In the next shot of Doug walking into the living room, the water bottle is gone.
Visible crew/equipment: When Doug and Carrie leave for their holiday, a stage light is reflected on the kitchen door. (00:09:30)
Factual error: Doug goes to the doctor for a check up after losing some weight. They live in New York, but the address on the outdoor sign is actually in California. (23101 Sherman Pl).
Continuity mistake: At the start, the distance the canoe has drifted changes instantly. And it changes a huge distance. (00:04:20)
Factual error: It is very obvious throughout the whole episode that the mountain scenery is that of California wilderness...the trees, plants and mountains look nothing like those in New York or the East Coast.
Continuity mistake: When Arthur asks Doug for a game of ping pong, the paddle is lying flat on the table. In the next shot there is a ball under the paddle which Arthur picks up (The ball is still on the table). In the next shot the paddle is back on the table and the ball is missing. (00:03:15)
Revealing mistake: When Doug snaps his bat it's very clear it is pre-broken. (Possibly from a previous take or to make it easier for Kevin James.) (00:07:55)
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.