When Diana comes into the room bearing a cup of tea, she has no wig in her hand, but when she leaves, she carries a blond wig, although there has not been a scene where she gets it.
In the beginning of the movie, during the fur coat fashion show, Diane goes out onto the porch to expose herself. When she first walks out, the top two buttons of her dress are unbuttoned. The scene cuts to a close-up of Diane and the top two buttons are now buttoned.
Towards the end of the movie, Lionel is shown beginning to blow up the canvas raft. He later explains that it is for Diane when he takes his final swim. Someone suffering from such extremely low lung function that he will only live a few months would never be able to inflate a raft that size.
One of the negatives that Mr. Arbus is developing is a Kodak T-MAX 400, which was not available in 1958.