#dianetics

Excalibur by L. Ron Hubbard (yes, that one) is actually by far the best-documented book on that lowest tier of the iceberg chart. Most of them are uncorroborated rumors at best.

It was an early, unpublished manuscript written by Hubbard in 1938, long before he founded Scientology, circa 1950-1953. Some of the information in this manuscript seems to have later been incorporated into his book Dianetics, as well as the follow-up book, which was also called Dianetics for some fucking reason.

Multiple credible individuals did actually read Excalibur, but there were also a number of ridiculous claims made about it, like how it allegedly drove certain readers insane. We can safely disregard those claims.