As Lisa and Marty smoke marijuana, the ash in Lisa's hair disappears and reappears between shots.
When Marty and Lisa are watching the music video, the same verse of the song "Forgot About Dre" repeats, i.e, the beginning of the song is heard twice.
The movie takes place in 1993 , yet Ali's mustang is a 1994 model.
Ali Willis states that she her baby is a boy. In real-life,her baby was a girl.
There are no anachronisms in the film. Yes the events depicted occurred in the early 1990's, but Larry Clark has stated that he set the film in 2000 so that he wouldn't have to worry about anachronisms. Also yes, the Mustang is not a 5.0. She isn't a car girl and doesn't know better. In the film she is even told that she is wrong, so that is a deliberate goof.
In real life, the events took place in 1993. However, several characters watch the music video for "Forgot About Dre," which was released in 2000. Additionally, the city of Weston is name-dropped twice, though it wasn't officially established until 1996. Finally, all of the actors wear late Nineties/early millennium fashion styles, hairstyles and make-up, as opposed to early Nineties styles, which are moderately different.
During the scene between Derek and Ms. Connelly, the boom is reflected in the window behind them, moving back and forth.
Ali constantly refers to her Mustang as a "5.0" which is completely impossible for two reasons. One has been pointed out, the 5.0 wasn't available in the 99 to 04 Mustangs, the last time a 5.0 was available in a Mustang was 94-95. To further this mistake Ali's Mustang isn't even represented by the V8 of that generation, but rather the v6 option.
In addition to Ali mistaking the Ford Mustang for a "5.0", even Bobby pointed out that she was wrong.