Oh yes, it was quite routine for novels, especially fantasy novels, to be presented in that form, as "This is a manuscript that was delivered to me" or "This is a tale that was told to me." Just about anything by Verne, Wells, or Burroughs is told in that way. And what I consider to be perhaps the first science-fiction novel, Gulliver's Travels
, was written as a satire of actual traveler's-tale accounts published by mariners and explorers in the period, and was meant to be published anonymously and passed off as nonfiction, though Swift's authorship was exposed shortly before publication.
Hmm. I guess that could count as the first spoiler.