In the film, the "Today" studio is set in it's present-day location (Studio 1A), where it has existed since 1994. During the time period Quiz Show takes place in, "Today" was located farther down the block in the same building, meaning there would be no windowed corner and no view of Rockefeller Plaza.
Early in the movie, we see the inside of the Barry-Enright offices, and a shot of the company logo, an interlocking B&E. That logo wasn't introduced until Jack Barry and Dan Enright reunited in the 1970s.
When Enright and Freedman attempt to convince Van Doren to appear on 21, they ask him how much does he think Bozo the Clown makes. Bozo's first TV show was in 1949 on Los Angeles's KTTV. However, Bozo did not gain national prominence until Larry Harmon established Bozo shows in various markets. The first was in LA in 1959, with the New York show also starting that year. Since Van Doren's conversation would have occurred in 1956, Bozo was not yet well known among adults or a high grossing star.
During the lunch scene, Goodwin describes the Reuben Sandwich as the only entirely invented sandwich entered in a sandwich contest by Reuben Kay. Some claim that a wholesale grocer named Reuben Kulakofsky created the sandwich at Omaha's Blackstone Hotel in 1925. However, Fern Snider, a waitress at the Blackstone, entered the recipe in a national sandwich competition in 1956, and won.
At the birthday party for his father, it shows a man dressed as a monk. This is supposed to represent Thomas Merton, a student of Mark Van Doren in the 1930s. However, Thomas Merton was not in New York until the 1960s, During this time period, he wrote to Mark Van Doren about his son Charles but was not in New York or Connecticut at the time.
Mark Van Doren mentions that he feels "like Leopold of Belgium, usurped by his son before his time." While true that Leopold abdicated the throne to his son, it was not because of any conspiracy or plotting from within his family, but because Leopold had become a very controversial figure after World War II and his decision to surrender to Nazi Germany in 1940. He spent six years in exile before requesting the Belgian Government to approve a law delegating royal powers to his son, Baudouin, then formally abdicated in 1951.
At the family birthday party, the father is slicing a white frosting layer cake. When his son unexpectedly visits later in the week he apologizes to his father for taking the last piece of cake. They both enjoy this last piece: a full chocolate with chocolate frosting cake.
Minutes before 'Twenty-One (1956-1958)' begins, viewers are seen turning on their TV sets, and a caption for the show comes on (instead of the previous program or some commercials). This may or may not be authentic, but after the quiz begins some late viewers turn on their TV sets, and they also get the static caption.