Years after the book and movie of Shirley's life was released, experts began to pick apart the story and find things that just didn't add up. For one, the book stated that "Sybil" had 16 different personalities. The book was not written in the style of a case study, but rather as a novel. Experts who interviewed Wilbur concluded that she had suggested MPD to Shirley, whom they thought of as simply a "suggestible hysteric".
In 2011, Debbie Nathan published a book titled Sybil Exposed, which documents what the author believes to be evidence that Wilbur, Shirley, and Flora made up the content of the book. She shows a letter that Shirley wrote in 1958 where she admits openly that she faked the "Multiples" for attention.
Cornelia Wilbur passed away in 1992. Shirley Mason was diagnosed with breast cancer in 1990, and the following year Parkinson's Disease. She passed away on 26 February 1998.