When Barbara confesses to Catcher in his apartment, they are both standing, but when Gwendolyn enters his apartment and races to Barbara after she over-hears Catcher say "Barbara Novak", Catcher is sitting on the edge of the bed.
After Barbara finds Catch in bed at Peter's party, she runs out of the apartment to the elevator where Catch finds her and it is revealed that he is still carrying around the other woman's hat though when we see him running around in previous shots there is no sign of a hat at all.
Barbara's book is shown being bought in a Russian bookstore. The book's cover is incorrectly written using the Latin alphabet, when it should be written using Cyrillic characters. Also the title is "Nyet Lyubof", which is grammatically not correct. It should be called "Nyet Lyubvi" (in reference to the title of the book in the movie) or "K chertu lyubof'" (in reference to the correct translation of the title, also the Russian title of the movie)
Catcher uses a remote control to turn off the TV when Barbara is interviewed. The Philco Predicta TV did not have a remote control.
Early in the film, Barbara and Vikki are in a taxi discussing her interview with Catcher Block. In the next scene, Catcher and Peter are traveling in a taxi on the same street. Although the background of both scenes begin different, near the end you can see they are the same. This is made obvious by the same doorway entrance, the same woman entering her car, and the same car order in both scenes.
When Barbara arrives in NY and encounters the bomb protesters in front of what appears to be the United Nations plaza, there is a prominent shot of the People's Republic of China (PRC) national flag on one of the flagpoles. PRC did not take over the UN's China seat from the Republic of China (Taiwan) until 1971; thus, in the early '60s, the Taiwanese flag would have been displayed.
In the opening sequence establishing the 1962 New York setting, the modern Canadian flag is among those flying outside the United Nations. In fact it did not replace the Canadian red ensign until 1965.
The New York City street-name signs were white-on-green, which in reality didn't occur until the early-1980s. Prior to this, the colors of the street-name signs depended on which borough of NYC you were in, and in Manhattan they were black-on-yellow.
Vikki tells Barbara that Judy Garland was a last-minute replacement for Soeur Sourire (aka "The Singing Nun") on The Toast of the Town (1948). The Singing Nun was an unknown in 1962, and did not appear on "Ed Sullivan" until 1964; Garland first appeared in 1966.
Catcher prepares for his date with Barbara to "Fly Me to the Moon" by Frank Sinatra, which was not released until 1964.
As Zip and Barbara are sitting on the couch at Peter's place, you can see the flickering lights that are creating the firelight illusion reflected on Barbara's wine glass.