Factual error: When Frank is in the bar/restaurant talking with coworkers, one of them remarks about "the old cubicle." Cubicles were not used in companies until the 1960s. In the 1950s, when the film takes place, companies had rows of desks without any dividers between them.
Factual error: Kate is wearing a watch with a Speidel Twist-O-Flex watch band. These bands were introduced in 1959.
Factual error: The wall phone in Frank and April's 1955 kitchen is an old rotary phone, but actually post 1980. It has a modern flat cord and a modern wire plug. Phones cords in 1955 were round and permanently attached to the handset with no square plug.