In 1957, when the White House is shown from a distance, a red Volkswagen bug drives by, with its white convertible top down. Several years later, in front of the courthouse in Tennessee, the same car is parked on the street, with the top down.
In fine dining, it is custom to set drinks from the right with your right hand, clear from the right with your right hand, and serve food from the left with your left hand. Several times throughout the film these customs were neglected, which seems strange for a staff of professional servers to do.
When the Freedom Bus is attacked and burned by a white mob, it happens at night on a bridge. In real life, the attack took place in the afternoon near a convenience store.
When his fellow butler clears Cecil's empty plate at the state dinner, he clears it from Cecil's left. Proper etiquette calls for dishes to be cleared from the diner's right side.
In their 1957 discussion about Emmett Till, Gloria Gaines says his killing happened "three years ago." Till actually was killed in 1955, two years before.
The Army major that shows up at the front door wears ribbons indicating he has been to Vietnam (including a Bronze Star commendation), yet does not wear a Combat Infantryman's Badge. Also, he and the other soldier wear the unit crest of the 101st Airborne Division, yet wear the patches of the Army's Training and Doctrine Command (TRADOC).
In close-ups toward the end, Forest Whitaker's crisp white collar has brown make-up along the edges.
When Cecil talks to Louis at the bus station, as Louis leaves for college, they walk through a motion-activated bi-part sliding door. The scene is set between 1957 and 1961. The first automatic sliding doors were invented in 1960, and were activated by stepping on a floor mat. Motion sensors were developed in the late 1980s.
In the White House scenes from 1957, the U.S. flag has 50 stars. Alaska and Hawaii became states in 1959, so the 1957 flag should have 48 stars.
The wall telephone in Cecil's kitchen has a modular jack and flat cord, introduced in the early 1970's. It should have a round cord hard-wired into the handset, like the phone in the front hall.
In the long shot of the White House dated 1957, the fence along Pennsylvania Avenue has concrete barriers. They were installed after the Beirut bombings in 1983. In a later scene, using an old film image, the barriers aren't there.
When the camera pans up Jacqueline Kennedy's legs after JFK's assassination, it's obvious that the actress is not wearing stockings/pantyhose. In 1963, no woman, especially the First Lady, would appear in public with bare legs.
When his fellow butler clears Cecil's empty plate at the state dinner, he clears it from Cecil's left. Proper etiquette calls for dishes to be cleared from the diner's right.