When Mr. Glass gets his first comic book on the playground bench in 1974, the cover of the book depicts as a backdrop the Philadelphia skyline, featuring predominantly Two Liberty Place, which was not built until 1990.
At several points they show comic book images which are supposed to be from the "silver age", the 1950s-1960s. However, the art displayed in them is not accurate for the period and is closer to the style predominant in the industry in the 1990s.
When Elijah Price goes from Franklin Field to the train station on South Street there is a post with a "Subway" sign at the top of the stairs. There is no subway running under South Street. It is a train station entrance. The subways in Philadelphia run under Broad and Market Streets with a spur line that goes to Camden, NJ. There is, also, the Frankfort Elevated Line.
Mr. Glass describes his disorder (Osteogenesis imperfecta). He describes the disorder as having 4 types each increasing in severity. At the time this movie was made only 4 types were identified. There are currently 8 types of the disorder identified as well as several subtypes.
David Dunn and a few other security guards are shown wearing FSU jackets and caps; this refers to the fictional Franklin State University where he works (the name derives from Franklin Field, the actual stadium name).
The goof items below may give away important plot points.
When David's son attempts to shoot David to prove David is unbreakable, David grabs the gun from the table using his left hand (with his wedding band on) in the close up shot, but in the master shot, we can see he used his right hand to grab the gun.
When David shares his identity with his son at the breakfast table, he pushes a newspaper toward him. In the close-up, the newspaper is folded into quarters, but in the wide-angle shot, it is clearly only folded in half.
When David follows the Orange Suit Man into the house, David goes upstairs and into a bedroom where he hears a whimper. In the master shot, the closet door where the children are held captive is cracked but in the following shot David is seen and heard opening the same door.
The criminal was killed by David, according to the newspaper article. But after he is strangled and lying on the floor he is still visibly breathing. This is a goof, unless David killed him later, or he slowly died from the choking after David had left, or the article was mistaken, all of which make little sense.