Factual error: In the scene where Mystery is playing "Rock & Roll All Nite" in the basement, Hawk is playing an Epiphone Special II guitar. The movie is set in 1978, and this guitar did not hit the market until 1996.
Factual error: One of the operetta excerpts shown in the movie is the humorous song "This Helmet I Suppose," during which Princess Ida's three brothers are supposed to remove their armor piece by piece, finding it heavy, hot and awkward. Partly as a result of this, the three are soon afterwards quickly and easily defeated in combat. In the film, however, only Arac, the brother singing the verses (played by Richard Temple (played by Timothy Spall)), removes his armor. The others simply stand still. (This might have made the battle scene end differently if it was shown on screen!)
Factual error: While Nate and his business associates are driving around in downtown Baltimore, the Key Bridge (which spans Baltimore harbor) is visible in the background. The movie was set in 1954; the Key Bridge was built in 1972, 18 years later. (01:33:55)