Revealing mistake: When Doug and Deacon are driving round trying to find Gabe's Pizzeria, they get into the car and pull out into the road. However if you look at the traffic, they would have hit at least 2 cars in doing so. But they don't, showing it's a projection. (00:14:40)
Revealing mistake: When Doug's mum is writing down the note about the T-11's, the writing is already on the pad. (00:14:40)
Revealing mistake: When Doug and Carrie are waiting in line at the DMV, a man (casting extra) can be seen just outside the doorway waiting to enter the scene. When the shot changes and Doug and Carrie approach the counter, the man casually enters the set. (00:03:30 - 00:04:00)
Revealing mistake: When Carrie is talking about going to the fertility clinic, you can see the fridge behind Doug through the door. If you look closely just before the camera changes a boom shadow moves across the fridge. (00:01:35)
Revealing mistake: During both opening and closing driving scenes, a light on the back and top of Doug and Carrie's heads slowly flickers on and off but never moves - revealing a stage light simulating driving past street lights. (00:00:20)
Revealing mistake: When the screen says "2 months later" the camera shakes. (00:21:20)
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.