When Brian and Neil break into coaches house. Niel goes in the left small window of a 3 window. When they cut to inside and Niel helps Brian into a single larger window.
When Neil and Wendy are sitting in front of the drive-in theater listening to the speaker, Wendy's hair is in ponytails. After some snow, her hair style turns to a normal cut and the ponytails are gone. In the next shot they return.
From the exterior, the curtains on the two windows where Neil and Brian enter the house appear different. The interior curtains match.
The teddy bear is propped in the corner of the sofa when Neil and Brian enter the living room. Brian manages to sit on it, however, a minute later, near the center of the sofa.
It appears that Joseph Gordon-Levitt wasn't wearing the blue contact lenses at the bus stop when Wendy's leaving for New York.
When Coach records the voice of Neil he presses the Rec and Play button simultaneously on his tape recorder, but you can clearly see how the Play button flips right back again thus making the recording impossible.
There is a Metallica "St. Anger" sticker (with the "St." torn
off) on the right rear fender of Eric's Gremlin in 1991. "St. Anger" wasn't released until 2003.
Car approaches traffic signal. Yellow light is a matrix of LEDs, but all yellow traffic lights in 1987 were incandescent bulbs.
Brian's room features a poster of Suicidal Tendencies' "The Art of Rebellion", which did not come out in 1991, when the events are taking place, but in 1992 (June).
When he arrives in Brighton Beach on a December night in 1991, Neil is seen noting where the closest subway stop is. The Brighton Beach station sign shows a Q in a yellow circle and a Q in a yellow diamond. But the "Q diamond" train was operating on that line for only a few years starting in the early 2000s. Prior to that, the Brighton Beach stop serviced the "Q circle" and the D trains.
Minivan and passenger car seen parked at 32:44 were manufactured after 2000.
The scene of Neal running in downtown New York after leaving his john with AIDS is actually Downtown Los Angeles.