How truthful?

I've been reading Carol McCleary's books about Nellie Bly - involving her in fictional escapades along with the likes of Jules Verne, Louis Pasteur, Sarah Bernhardt, and Frederick Selous (who? you may ask; I did). They footnoted him and showed a photo, so you couldn't suspect him, though Nellie does; he was very famous in his day and was the inspiration for Alan Quartermain... and thus a forerunner of Indiana Jones. I like them (though the second book is much better than the first).

I was charmed from the preface, though. How can you not like an author who tells you:

The reader may rest assured that they may compare our truth and veracity to that attributed to that lioness of literature, Lillian Hellman, by none other than author Mary McCarthy.

(In case you don't know the story, the latter said of the former (prompting a lawsuit): Every word she writes is a lie, including and and the.)