I'm not so sure of that (no meeting of the minds) Toledano (from the article) appears to have written a career bio of Felt, just plain-old agent Felt, that few would likely care about w/o the "Deep Throat" association. Orig bio: 1979. "DT" connection admitted/established 2005 in Vanity Fair. 25-26 years. I could see some Statute of Limitations/Laches issues wrt Toledanos' rights to the much-improved valuation of the book with this new knowledge. But I'm not a lawyer so I guess we'll just have to see.
Imagine you are a manufacturer of baseballs. You make zillions of them. Barry Bonds hits one of yours over the fence for #715. Do you have rights to that ball?
I don't think the analogy is apt.
Sure, the man wrote a garden-variety biography. But then Felt purchased the rights to all future money from the biography, and the writer SOLD those rights. Sure, the writer had no idea the book would have value, but Felt DID know he was deep throat, and therefore knew, or should have known, that the value of the rights to the biography were much more valuable than what he offered.
I presume the writer had specifically asked Felt if he was deep throat, and Felt lied to him about it. And it's probably in writing. That lie was about a material fact effecting the value of the rights to the book.
I don't know if the statute of limitations apply. Almost everything I know about this area of law I learned watching a 5-part series on a local college educational channel, so any good lawyer might know more about this than I do.