Queasy Rider - S2-E1
Other mistake: Arthur gives his CV to Doug at the start. You can see it's typed but both Doug and Arthur talk about it being in magic marker. (00:00:30)
Queasy Rider - S2-E1
Other mistake: When Arthur is telling Doug that he had a bike, you can see and hear a bright light switch on in front of them.
Other mistake: When Doug is drawing a picture to explain to the nurse why he is there, a man purchases a beverage from the "Hot Drinks" machine behind Doug. The drink is ready unrealistically fast and the man immediately takes a sip from an obviously empty cup. Those machines produce notoriously hot beverages, so if the machine actually worked the man would have scalded himself.
Other mistake: Carrie describes Susie as "one of her best friends." Earlier in this same season, the episode "Female Problems" was about her not having friends anymore. In fact, in that episode, she spent a whole evening calling any former friend that she could think of. She told Doug that they all had babies, hated her, or she hated them.
Frozen Pop - S2-E15
Other mistake: When Arthur decides to sleep upstairs instead of downstairs, he brings along a can of beans for a snack. It then cuts to an exterior street shot, which should be somewhere in Queens where the Heffernans live, but instead it's a shot of the corner at 14 Ave and 73 St in Brooklyn (some areas of Brooklyn and Queens may appear similar). Next shot is inside the Heffernan house in Queens. (00:11:45)
Other mistake: When Doug and Carrie go to visit the new neighbour, Jessica, Carrie tells her that they live at #8013; however many other episodes we see the numbers 3121 on the Heffernan's door and later learn that the Heffernan's live at 3121 Aberdeen Street in Rego Park. (00:28:35 - 00:29:35)
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.