The morning after Frank and April decide to move to Paris, Frank leaves the house wearing a dark red tie. He wears the same tie in the office, when he tells the boys he's moving. Frank's tie is light yellow at lunch; in fact, everyone's tie is different. When he gets back to the office, his tie is red.
After John Givings' tirade to April and Frank Wheeler, Frank angrily walks from the dinner table to the opposite corner of the room. In the next shot, he is standing in the corner diagonally across of the room, sipping his drink.
When Frank and Mr. Pollock are having lunch in the restaurant, the arrangement of the food on Mr. Pollock's plate changes in each shot.
After Frank leaves the hospital, he runs past the same 1955 Packard Constellation three times.
When April comes down the stairs at the end, she is wearing stockings. When she is standing looking out the window and she looks down at the blood, her feet are bare.
Grand Central Station has only allowed electric locomotives since long before the 1950s. The train Frank takes to work is pulled by an Alco RS-3 diesel locomotive, which does not have dual diesel/electric power capability.
The masses of male commuters shown at the beginning all wear hats. In reality more than half of them would have been bareheaded. Ads by hat makers in the mid 1950s (see old Life magazine online, for example) were desperately pleading with men to go back to the custom of wearing a hat; I can also testify from personal memory that at that time in downtown Manhattan most men who worked in offices went about hatless. Had the scenes been set in winter, the men in overcoats etc, a few more head coverings would have been realistic. But not many. The mid-fifties, between the age of the hat and the age of the baseball cap, were the great age of bare-headedness.
The depiction of Grand Central station packed with uniform masses of office workers was itself unrealistic. Even during rush hour, any snapshot of the crowd there would have included a more heterogeneous crowd of people, different ages, different occupations, male and female.
The magazines in the Wheelers' living room, and Frank's Berlitz guidebook, are dog-eared and browned. They're probably from 1955, but they look like they're 50 or 60 years old.
When April reached for the car door handle, her hand reached where today's car handles are located. She then had to move her hand up to the handle for an older car.
April smokes Marlboro Lights, which were introduced in 1977.
During the opening sequence, an establishing shot shows the Manhattan Bridge. The Verrazano Narrows Bridge is far in the background, even though it was completed in November 1964.
The kitchen has a 3-prong electrical outlet. In the 1950s, American homes had 2-prong outlets.
At lunch, a co-worker tells Frank he will be "sorely missed in the old cubicle." Cubicles were introduced in the mid-1960s by Herman Miller Inc., a manufacturer of office furniture.
The light switches are post 1970s.
When April shows Paris on the globe, the borders of the European countries are current. Most notably, the reunified Germany is visible, with the borders it did not have until 1990.