When Felix is riding the subway while observing a rider with lesions, the subway car is immaculately clean and graffiti free. During the early-1980s (the time this film takes place), New York City subway cars were notoriously gritty looking with graffiti covering the inside and outside of the cars. Police officers were also a common sight as crime on the subway was at an all time high. During the late 1980s, the Metropolitan Transportation Authority (MTA) which oversaw the city's subway services purchased a newer model from Canadian manufacturer Bombardier that was made of graffiti-proof alloys and had a different seat layout from previous trains. This model is the one used in this film.
In the house at Fire Island a Baseball game is seen on the TV which Bruce mentions. In the summer of 1981 however there was a long MLB strike from June 12th through August 9th, 1981 during which time that scene presumably is set and no games were played.
The condition of Felix's teeth change drastically between 2 scenes that took place on the same day. In the scene where Felix and Ned get married when Felix smiles his teeth are grayish in color and noticeably decaying, but in the scene right before that when Felix goes to see Ned's brother to discuss his will his teeth are whiter with no signs of decaying.