Continuity mistake: When driving the Mini, the cars around them are constantly changing. (00:12:05)
Revealing mistake: When driving the Mini, the reflection on the bonnet never changes despite being on the highway. (00:12:00)
Visible crew/equipment: When Richie is explaining about getting rid of the car, tape markers are visible by Doug's feet. (00:14:40)
Visible crew/equipment: After the first drive in the Mini, a stage light is reflected clear as day in the bonnet. (00:13:20)
Continuity mistake: When making a PB&J sandwich, the jar of peanut butter rotates by itself. Note the label. (00:09:30)
Revealing mistake: When Doug stops to tie his shoe outside the car dealership and Carrie walks up to grab him, you can see the fake back-drop sway with her motion. (00:08:35)
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.