It only appears that Betty is not wearing her purple hat after graduation. As she walks down the steps her hair hides the cap but when she says, "Excuse me Mother," the cap is noticeable. Since the first part of the scene is filmed in one shot it is impossible that she just put it on. However, there are inconsistencies with her curls throughout the entire graduation scene.
At the wedding, champagne is served in flute glasses. They were rarely used until the 1970s, when drier vintages became preferred. In the 1950s, champagne was served in champagne coupe (or saucer) glasses. They are still used in champagne fountains at weddings.
During the slide show, Dr. Watson says "A Rhodes scholar. I wonder if she recites Geoffrey Chaucer while she presses her husband's shirts". Women were not permitted to apply for Rhodes scholarships until 1977.
The china Nancy Abbey uses for her etiquette class, "Prince Regent" by Royal Worcester, is inspired by an 1811 pattern privately commissioned by George IV as Prince Regent. However, it was not produced for public sale until the 1990s.
When Nancy Abbey watches I Love Lucy, the title card shows the famous heart-on-velvet, which was only used when the show was in syndication. The original opening sequence featured ads for a cigarette company.
When Katherine walks along the outdoor corridor with the tile floor and columns, before Bill gives her the belated Christmas present, puddles are clearly visible. In a close-up view, when Bill gives Katherine her gift, the tile floor is completely dry.
At the Adam's Rib party, Giselle is sitting in the window, with her hair parted in the middle and her forehead visible. In the next shot, when she moves into the room, her hair is parted on one side and sweeping across her forehead.
With the exception of Christmas break, all the bar scenes are similar. Bill wears the same sweater, Katherine's hair is always half-up, her earrings are the same, and her outfit is the same, with either a coat or a vest.
The night Giselle shows off her new diaphragm is the same night Betty mentions that her wedding is three weeks away, on November 2nd. This would set the scene sometime in the second week of October. This is further proven when, a few scenes later, Amanda Armstrong's termination letter is dated October 10th. But when Katherine pins Betty's article on her bulletin board, the article is dated September 19th.