Factual error: The opening shot (of the New York Stock Exchange's trading floor) has the subtitle "1985," which might lead one to expect that at least the action in the first few scenes takes place in the year 1985. However, when Charlie Sheen is talking to his Nimrod broker buddy the Nimrod jokes that the day the Challenger exploded, Gekko was on the phone "selling NASA stock short." The Challenger exploded in January, 1986, not 1985. [An explanation for this: Wall Street, as conceived and filmed, was supposed to be set in 1987. However, near the end of 1986, The Ivan Boaesky insider-trading scandal hit, many rules were changed, and acknowledging those events would have undone much of the plotting of the movie. So the movie was shifted back in time to 1985 (before the scandals, and also before the Challenger disaster), thus creating this major goof].
Factual error: After Bud's conversation with Gordon in the park he goes to a restaurant bathroom. The agents are waiting for him. He open his shirt, they rip the tape recorder off of him then immediately begin to play the conversation. It picks up right where the evidence is. No one had time to rewind the tape.
Factual error: Following the tavern scene with his father, Bud wakes up early and loads a calendar on his computer: Monday 6 May 1985. Later that day at Jackson Steinem and Co, Marvin says "Buddy, got tickets to the Knicks game tonight. Go out and cruise some chicks afterwards, this is gonna be awesome, whaddya say?" Inviting him to a New York Knicks NBA basketball game. However on that day the Knicks never played, and secondly the playoffs had begun - by finishing second-last in the Eastern Conference, New York were eliminated from making the playoffs.