Anachronisms: Joyce comes by train from Delaware to Cleveland to meet Harvey in 1984. However, the Genesis engine shown pulling the train did not enter Amtrak's fleet until 1993, and the Amtrak logo on the engine is the post-Acela version, introduced in 2000.
Anachronisms: In the establishing Manhattan skyline shot before one of the Letterman sequences, what was then (the 1980s) the Pan Am building is shown with its current "Met Life" signs (which didn't replace the "Pan Am" signs until 1992) shining from the top.
Revealing mistakes: When Harvey forgets his keys and cannot get into the apartment, the elderly woman opens the door for him. When he closes the door behind him, it bounces off the frame and doesn't latch shut.
Anachronisms: The sign outside the hospital where Harvey works refers to the "Department of Veterans Affairs". The "Veterans Administration" did not become the Department of Veterans Affairs until 1989.
Continuity: When the real Harvey is recording his voice-over, someone fills his "orange soda" to the top of his glass. When he picks it up, there is less than half a glass of soda.
Anachronisms: When Joyce is running through her personality disorder diagnoses, before she says her "delusions of grandeur" line, we see the phone and an open Fruit Cup near it. The scene is set in the 1980s, and the plastic fruit cups weren't on store shelves until the late-'90s or early 2000s.
Anachronisms: In Joyce Brabner's comic book shop in Delaware, she is looking for the new issue of American Splendor, issue #8. American Splendor #8 was published in 1983. There are several promotional posters on the wall of the comics character Concrete (the black, white, and yellow ones that say "Can't find what you're looking for? Just Ask!"). The first Concrete story was not first published until 1986. (The poster wasn't released until much later.)
Factual errors: 38m00s into the DVD, there's a girl and a guy working in a comic store arguing about saving one issue aside for her whereas he sold all of them. Behind her are comics in protective covers, but standing upright on the wall on very thin shelves. A real comic store would affix the bags at the top edge, hanging them on the wall so that gravity doesn't cause the comics to "limp" and sag.
Anachronisms: The red and white Ohio license plate on Toby's station wagon was actually in use during the years of 1976-1979. Since he was going to see "Revenge of the Nerds" which was released in 1984, the correct Ohio license plate for the time period would have been blue lettering on a white background which was issued during 1980-1984.
Anachronisms: The opening of the movie is set in 1975. During the opening credits, there is a scene that has CSX freight cars in the background. The CSX corporations was formed in 1980, five years later.
Continuity: During the scene in Shay's restaurant, the level of the soda in Harvey's cup fluctuates between half full and completely full at least twice.
Continuity: The exterior front of the comic book store shows a wooden structure with windows that reach about half way up the height of the building and a wooden door with a glass section in it. The interior view shows glass extending from the ceiling to the floor and no wooden door.