What is the full story that neither Mrs. Slade nor Mrs. Ansley knows?

In Edith Wharton's "Roman Fever," both Mrs. Slade and Mrs. Ansley have incomplete information of the events that took place years ago in Rome that one moonlit night. Mrs. Slade feels she has the upper hand because she knows that she and not Delphin, her fiancé, wrote the letter to Mrs. Ansley. However, Mrs. Ansley knows the bigger secret--that she did actually go to meet Delphin and had his daughter. The full story is the combination of both women's stories and secrets. Wharton masterfully uses the symbol of knitting to show how the stop threads or details are woven together to make a complete story. The irony is that each woman feels as if she has the upper hand because she knows the story, but they later find out that each only knows part of the story.