According to the DVD commentary by Aubrey Solomon, "When the real Eve signed the contract for the movie, the studio had her sign three separate contracts under each of her personalities, so that they would be covered from any possible legal action. In fact, when she signed the contract, they actually had her go into the personalities, and the signatures were all different on the contracts."
In her 1977 book, "I'm Eve," Christine Costner Sizemore, the real-life woman on whom the character of "Eve" was based, said that she had really had 26 multiple personalities, not just three; and that the popularity of the book and movie based on her life had only traumatized her further because Dr. Corbett Thigpen had forced her to sign over all rights to her story to him. Contrary to this statement, Dr. Corbett Thigpen made personally sure that Mrs. Sizemore was given her fair share of any and all profit from the movie, for which there is paper-trail proof for any in doubt. Furthermore, Dr. Thigpen and Mrs. Sizemore were on good terms with each other before Dr. Thigpen passed away in 1999, if he had done her wrong, that would not have been the case.
This story of Multiple Personalty Disorder was followed in 1976 by "Sybil" another story of multiple personalities. Joanne Woodward, who played Eve with the three personalities, was cast as Dr. Wilbur, the psychiatrist who treats Sybil.
The reason for Eve's personality split as depicted in the film is complete fiction. According to a People magazine article in 1989, "As a 2-year-old, Eve had witnessed three unnerving scenarios within three months: a drowned man being pulled from a ditch, a sawmill worker sliced into three pieces and her own mother cutting herself severely on a piece of broken glass. Too young to deal directly with what she had seen, she developed the first in a line of alternative personalities, including the three that now revealed themselves, one by one, to the amazed [psychiatrist who diagnosed her as having multiple personality disorder]."
In 1980 the British rock band Siouxsie and the Banshees recorded "Christine," a song based on the same case of multiple personality dramatized in "The Three Faces of Eve". The 'B' Side of the single was called "Eve White/Eve Black"
The three literary works that Eve quotes from are "They Are All Gone into the World of Light" by Henry Vaughan ('Dear beauteous death ...'), "Locksley Hall" by Alfred Lord Tennyson ("Love took up the glass of time...") and "Two Noble Kinsmen" by William Shakespeare ('This world's a city full of straying streets ...').