Other mistake: The movie starts in September 1961 and we are told that the talent show is in June. During the talent show there's a big banner saying 1961 when it should read 1962.
Other mistake: Eugene is suspended above the stage with the box of paper leaves and snowflakes ready to throw them down at the correct moments; but when the Fall section of Girl For All Seasons is on he doesn't throw any leaves. Also, the amount of snow coming down over the stage at the Winter section is completely disproportionate to how widely and evenly Eugene could distribute it.
Other mistake: When Michael is sitting down singing the song "Charades," there is a window behind him. Dolores comes up to the window and waves for the Pink Ladies to come outside. First you see Paulette go by, then Sharon, and the third girl is obviously supposed to be Rhonda, as she is wearing a Pink Lady jacket. If you look at "Rhonda's" face, you can see it is not Alison Price, who portrays Rhonda throughout the rest of the movie. (01:22:00)
Other mistake: During the bike chase at the bowling alley, when the line "don't know who you are" is sung, a guy on a car hood throws his body to the right as if he were pushed by an invisible hand but in the next shot he repeats the motion when a bike hits the car he's sitting on.