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)
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)
No Retreat - S4-E5
Other mistake: In the opening scene when Doug is cooking hotdogs for his friends, the smoke coming from the BBQ is very fake. (00:00:20)
Other mistake: At the end when Doug takes the bandages off Carrie's face, the bandages come off far too easily as if they weren't really attached in the first place.
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.