Character mistake: Annie when giving her gifts is holding two little mini flags to cover the possible ethnicity of Shirley's baby. One is a Chinese flag and the other is Zimbabwe. Annie makes reference to the fact that the ethnic food she made is one from Ghana. She makes Ghana ethnic food but does not get the right flag for Ghana. She decorates the table with numerous flags which are also Zimbabwe.
Character mistake: At the party, Jeff is talking to Ted about his parents' divorce, which included a custody hearing. Jeff mentions the divorce lawyer drove a Mercedes SLK. However, the SLK didn't come out until 1996, which would make Jeff at least 21 (turning 22) at the time of the divorce (he was born Nov 1974). There would have been no need for a custody hearing (Jeff was an only child between his mom and dad) and his parents divorced when he was very young, so the divorce had to happen prior to 1996.
Character mistake: In the bonus clip where we see Leonard's online video about frozen food, the first thing he says is, "This is November 29th". However, if you look under the video, you can see the video was uploaded on Nov 26, 2011, which is three days earlier.