Visible crew/equipment: When the camera cuts into the wide shot of Carrie leaving the store, the camera rig to the left of the screen is almost entirely visible. You can see it follow Carrie around for a good 10 seconds. (00:10:35)
Continuity mistake: The second time we see Doug's disk, it is spinning. In one shot it is spinning in shadow, but in the second shot it is in the sunlight. (00:08:00)
Visible crew/equipment: When we see Arthur playing Shuttleboard for the first time, his mic pack is visible. (00:08:00)
Continuity mistake: During the first shuffleboard scene, the characters are brightly lit and cast by long dark shadows (indicating early morning or late afternoon), but when you see shots of the shuffle pucks flying into the bleachers, the bleachers' and extras' shadows are cast straight down (indicating noon hour).
Continuity mistake: When they are in the kitchen Carrie's purse switches from shoulder to shoulder when she tells Doug the good news.
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.