After reading Lucy's comment yesterday, I decided to look into the whole Bell Jar thing. Sylvia Plath's novel was published in England, where she was a resident, in January of 1963, just a few weeks before she committed suicide. She didn't want her roman a clef to be released in the United States because she was afraid too many people would be hurt by it, so it was not published here, although imported and bootleg editions sold well in NYC bookstores.
Due to some quirk of international publishing copyright law (since changed), which had to do with an author failing to secure overseas publication within six months of a book's being published, an American publisher could publish its own edition of The Bell Jar after a certain amount of time had passed. I don't think the novel fell into public domain; I just think it means someone could publish it without anyone's permission, but still have to pay royalties. Which is exactly what Random House planned to do in 1971, until someone at Plath's British publishing house prevailed upon them to go through the proper channels. I believe Random secured the permission, if not the blessing, of Ted Hughes, and the American edition of The Bell Jar is indeed authorized by Sylvia Plath's estate.
My favorite college professor told one of my classes that The Bell Jar was a fine novel that no teenage girl should ever be allowed to read. I've yet to read it myself.