In her Secret Doctrine, Helena Blavatsky claimed that she had unique access to ancient texts known as the Book of Dzyan. These texts were guarded by a dedicated brotherhood in Tibet, unknown to ethnology, and written in a language unknown to science--but not to Blavatsky!
[These are] the records of a people unknown to ethnology; it is claimed that they are written in a tongue absent from the nomenclature of languages and dialects with which philology is acquainted; they are said to emanate from a source (Occultism) repudiated by science; and, finally, they are offered through an agency, incessantly discredited before the world by all those who hate unwelcome truths, or have some special hobby of their own to defend.
Blavatsky, translator extraordinaire, managed to translate these secret texts and, what's more, reveal them to the book-buying public without a hint of protest from the secret brotherhood.
Ditto "Col." James Churchward. He claimed that he learned about the history of the lost continent of Mu from yet another secret brotherhood, this time in India, composed of the only three people who could still read the Muvian language of Naacal. One of these three gave lessons to Churchward, who then miraculously translated an entire history of the lost continent from the surviving fragments of the Naacal tablets.
But Churchward's lost continent and Blavatsky's spiritual poetry pale in comparison to the claims of Joseph Smith a century earlier. As is well known, the founder of Mormonism claimed that an angel named Moroni showed him gold tablets that Smith miraculously translated into the Book of Mormon, yet another half-baked pseudo-history of the ancient past.
In all three cases, curiously enough, the original tablets and texts disappeared and have never been found. (What a shock.) Therefore, it was no surprise when in the 1970s, in Gold of the Gods, Erich von Daniken claimed to have found a library of gold tablets on which the aliens had written their entire history in a lost language and then buried it in a cave in Ecuador. Of course every expedition to von Daniken's supposed cave turned up nothing and the author admitted he had made the whole thing up.