Window Pain - S5-E2
Visible crew/equipment: When Doug gets into their Jeep after meeting the new neighbours, a man and the backstage can be seen in the passenger side mirror. When the shot cuts back to Doug again it's darker but when he backs up, the reverse lights of the Jeep reveal the man and stage again. (00:26:55)
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)
Window Pain - S5-E2
Continuity mistake: When Carrie and Doug are having the discussion about the dry cleaning, the way Carrie is holding it changes instantly. (00:06:10)
Window Pain - S5-E2
Continuity mistake: When Doug and Carrie are arguing outside the neighbour's house, Doug takes a big swig from the Scotch bottle and then puts it on the ground. After the police pull up, the shot cuts back to Doug and Carrie. Doug picks up the bottle from the neighbour's porch railing. (00:42:45)
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.