Continuity mistake: At the party when Winston and Coach are talking to the two women and Nick walks up, the girl that says it's hot and starts removing her jacket, almost completely off in that shot. But then it cuts and cuts back and her jacket is almost entirely on, and she starts taking it off again.
Continuity mistake: Jess is talking to Rachel about Nick's new girlfriend and the back of Schmidt's head is seen, where he has been standing behind Ceca the entire time. The in the very next shot, Schmidt is impossibly sitting back in his seat on the other side of the table he just was. (00:14:10)
Continuity mistake: When Schmidt and Robbie are spying on Cece's date, Schmidt sits down at Robbie's table to his left and after they both admit that they are still in love with her they bring it in for a hug. Cece walks over to confront them and they are still embracing each other, but they have suddenly switched places and Schmidt is on the right and Robbie is on the left.
Other mistake: In the beginning when Jess is showing the guys her outfit for Cece's party, you can see she is wearing blue platform high heels. She walks in them just fine. But the next day, when she's filling in for Cece, she's given platform high heels and can't walk in them at all. (00:02:37 - 00:15:17)
Factual error: S3E01, "All In", reveals that Winston is colorblind, seeing green as brown. But later in the series, Winston becomes a cop, working for the LAPD. This wouldn't have happened because candidates for the LAPD are put through a color blindness test where they are required to quickly and accurately identify colors. Winston would have failed and would not have been allowed to join the LAPD.
Revealing mistake: In the pilot, the exterior of a bar is shown as a scene transition. While the show takes place in Los Angeles, the bar and street intersection shown are in Providence, Rhode Island. You can see a banner with the word Providence in the shot and the street names match the intersection.
Other mistake: In 5x04 'No Girl' at the end of the episode Brandon is wearing Jess' dress and shows a red, black and white striped dress which Schmidt and Nick say they like. At the end of 5x05 when they're shouting to Jess in the hotel room, she's seen in this exact dress, but she's meant to be sequestered, so would have had no way to get the dress as it wasn't packed. (00:21:18)
Factual error: There is no HDMI plugged in to the TV, which is accurate for there being no input detected when Coach turns it on to watch the game, but Jess cuts a coaxial cable that is plugged directly into the TV. The input should have been on the Live TV/Antenna/Over-the-Air/Channels input if that's how they watch TV. (00:15:29)