As Monica is putting the needle on an Elvis Costello record, there are two albums propped up against the wall behind the turntable: "My Aim is True" and "Armed Forces". In the next shot, they are gone.
When Caitlyn and Bridget are talking to the bartender (when he tells them he's a law student) Bridget's straps switch from on her shoulders and off her shoulders.
In the taxicab, the reflected light from the disco ball appears to be spinning in a different direction when we see the passengers from when the driver is shown.
In the taxi cab when the taxi driver is talking to the two women looking for dates, the lights from the disco ball are rotating one way on the women and then in the next shot, it is seen rotating the other way on the taxi driver.
While the two girls from Lake Ronkonkoma say they need to catch the last train, and the trains run 24/7, they are using that as an exit line.
This movie is set during New Years in the dead of winter, yet there is no snow, the people's breath is not visible, and people are not dressed at all for winter weather.
Although apparently set on New Year's Eve 1981, numerous automobile designs that were introduced well after 1981 are visible in various shots.
The beer that the punk kids offer to Val and her friend is Miller Genuine Draft, a brand of beer that was not introduced until well after 1981.
In one of the club scenes, a patch on a dancers jacket can be seen briefly on the left side of the screen. This is an "Anti-You" O.J. Symptoms patch. The OJ Symptoms were a punk band in the mid '90s.
The song playing during the opening credits, Bow Wow Wow's version of "I Want Candy", which was also the video playing on the TV behind Ben Affleck in the bar, wasn't released until the next year, 1982.
The word "yuppie" first appeared in print in March 1983 and didn't become commonplace until after the publication of "The Yuppie Handbook" later that year. Two characters in 1981 describe the law student/bartender as a "yuppie".
When Val and Stephie cross from Avenue A to Avenue B they are on Avenue B and 9th. There is no 9th Street between A and B. Tompkins Square Park covers A to B between 7th and 10th Streets.