Factual error: A hard pack of Winston cigarettes is shown, but these were not available in 1953.
Factual error: When we hear Doris Day singing "Secret Love" the record we see on the turntable has an RCA Victor label visible/readable. Doris Day songs were released on Columbia Records.
Factual error: When Julia Roberts and her roommate are in their living room and "I Love Lucy" comes on the TV, the opening theme song is accompanied by the traditional heart with "I Love Lucy" written on it. However, this movie takes place in 1953-1954, and that opening for the show wasn't used until the show was put in syndication many years later. During the show's primary run, cartoon characters of Lucy and Ricky opened the show. (00:13:50)
Continuity mistake: When Julia Roberts is sitting on the couch with the male teacher, after he pours her a drink, they move the camera and show her and her drink is almost empty and then they show him and the drink is almost full. They then repeat going from her with an almost empty glass to him with her glass almost full.
Other mistake: In the scene where Betty and Joan are in the kitchen after dinner, we see the coffee percolating in the pot but never see Betty pour the coffee into the china pot before taking the tray into the living room.
Factual error: In the scene with the big band, the band is playing a tune in which the trumpets play the melody with a muted sound (this is kind of a "metallic" sound) yet the trumpeters don't have any mutes in their horns. They would have to be awfully good players to be able to make their trumpets sound like they are using metal mutes if there were none available. This is basically an impossibility.
Audio problem: When Joanie and Tommy are eating dinner at Betty's home, there's a close-up profile shot of both Joanie and Tommy right before they kiss. Tommy says to Joanie, "Come here you," but his lips don't move.
Continuity mistake: During an outdoor campus celebration, students dance around a May Pole, winding ribbons attached at the top around it. The ribbons are wrapped around the pole about five inches from the top. In the next shot, the ribbons are not yet wound around the pole as the girls circle it. (01:23:00)
Continuity mistake: When Kirsten Dunst is getting married, and the bride and groom are having their photos taken, they talk about reading a poem, and Dunst hands over a piece of paper with the poem written down on it to her husband. When he takes it, he carries on holding her hand, but in the next shot, when a photo is taken, both characters' hands are down by their sides.
Factual error: The Waterford Castlemaine crystal pattern used for the etiquette lesson, and later in the house Julia Roberts lived in, did not exist in 1953. It was introduced in 1986. (00:27:50)
Continuity mistake: In the scene where Dunbar gives Katherine her Christmas gift, the brick path that Katherine is walking on is wet and covered by ice and snow. When we have a closeup of Dunbar catching up with Katherine, the path is dry and has no snow or ice on it. (01:11:25)
Factual error: Joan gets accepted to Yale school of law in 1954, but Yale didn't accept women students until 1969.
Other mistake: Betty's mom is requesting a change in the table setting, eg. no candlesticks, glassware trimmed with gold etc. You then see the actual wedding happening and see candlesticks and glassware without the gold rim.
Other mistake: When the girls are sitting in the common room on the night Giselle shows them the contraceptive, Betty says, "Do you realise November 2nd is three weeks from now?" Yet, the University newspaper with Betty's nasty editorial shown on screen the next day is dated September 19th. (00:18:43 - 00:23:53)
Continuity mistake: At Betty's wedding where Dunbar has just joined Katherine et al. at their table, Nancy gets up and makes her way round the table to ask Katherine if she wants anything from the bar. We see her arrive between Katherine and Dunbar. However in the next shot, she isn't there. It isn't until a few seconds later that she seems to appear again. (00:37:20)
Answer: The colour change every year and the number is the year they finish (Joan's hat says 54 and their last year is 1954 as Nancy says around new year.)