Tons of individual books have authors whose true identities are not known, or at least not positive. Thousands of cheap paperbacks were ground out from the 40s on. If you want to go back further, the same problem applies to hundreds, maybe thousands, of pulp stories. Most of the less respectable ones were written under pseudonyms or house names. A lot of progress has been made in matching titles to real names, but that hasn’t been done for all. Even higher-class erotica like The Olympia Press has a few authors whose identities aren’t certain. A woman using the pseudonym of Ataullah Mardaan wrote Kama Houri and Deva-Desi, now rare collectibles. Publisher Maurice Girodias swore she was a real person, but no trace of her has ever surfaced. Most people think that one of his regulars wrote the book. If she is real, her name went to the grave with them.
There are some tricky identity problems even where the author is known. Take the case of Lewis Padgett. That’s known to be one of the joint pseudonyms that sf writers Henry Kuttner and C. L. Moore used after they married. Except that we also know that they didn’t always work on the same story that got sent out as a Padgett. For the paperback reprint of Robots Have No Tails, Moore wrote an introduction stating flatly that she never wrote a word of any of those stories. What about the rest of their “joint” work? Some are known, most aren’t.
Salvatore Lambino legally changed his name to Evan Hunter in 1952. He revealed he was Ed McBain as early as 1958. But he was also Hunt Collins, Curt Cannon, Richard Marsten, Ezra Hannon, and John Abbott. And nobody knows if he wrote any books as Dean Hudson, which is a great example of the point I made above:
That footnote goes to an Earl Kemp article that discusses the controversy and the denial. It’s great reading. Click over there now.