Continuity mistake: When Doug and Richie are waiting for Spence at the pub, there is a pepper shaker in front of Doug's beer that disappears and reappears. This happens again again after Spence arrives and Rickie is making fun of him. (00:04:15)
Continuity mistake: Right at the start, the salad cutlery keeps crossing and uncrossing itself. (00:01:05)
Other mistake: Carrie describes Susie as "one of her best friends." Earlier in this same season, the episode "Female Problems" was about her not having friends anymore. In fact, in that episode, she spent a whole evening calling any former friend that she could think of. She told Doug that they all had babies, hated her, or she hated them.
Continuity mistake: When Doug and Ritchie are waiting for Spence, the amount of beer in Doug's glass keeps changing. (00:04:30)
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.