Sorry for the delay in responding. I was relying on my memory. Now I’ve acquired a copy of the 12/TWELVE /Hachette Book Group (mass market paperback) November 2015 edition of 13 HOURS-The Inside Account of What Really Happened in Benghazi. Its copyright (data) page (unnumbered iv) has as its FIRST sentence, “This book i a work of fiction.” On page xiv, in A Note to the Reader, says, “Although written as a narrative, this is a work of nonfiction.”
Weird. I tried to see if I could find the copyright page online somewhere, but couldn’t: the preview version available on Amazon only shows the (earlier) hardback edition of the book, and it does not contain that sentence claiming that the book is a work of fiction.
A sentence like that is a pretty standard disclaimer in books that are, in fact, sold as fiction (i.e. novels), but I don’t know why it would be in a work of nonfiction. I’d be suspicious that it was added as a C.Y.A. against charges that the book was full of made-up stuff.
Creative nonfiction is nonfiction, but there will be fictional elements introduced for purposes of entertainment which necessitate a disclaimer. The genre is relatively new and creative nonfictional works can be hard to categorize which can lead to conflicting descriptors as you see with this book.
“Creative nonfiction” under whatever name has been around since at least 1965, with the publication of Tom Wolfe’s “The Kandy-Kolored Tangerine-Flake Streamline Baby,” a collection of short pieces which predate, of course, the book. No doubt others can point to even earlier examples.
I would think every work of non-fiction from pre-enlightenment Europe/Middle East fit into the same category. The works of Julius Ceasar or the Bible, for example, purport to be true, and mostly detail the facts at the authors believed them to be. However they also contain many elements that were just plain made up for the purposes of entertainment or to illustrate a point.
Rather than looking for earlier works of creative non-fiction, it would be more profitable to look for the first example of pure non-fiction. Until quite recently every work of non-fiction introduced fictional elements, and the reader expected that to be the case. Nonetheless the Bible or the works of Caesar are generally listed as non-fiction works.