Have you seen G. Filbert's list of entities and beings?I have a background in both scientology and magick. All I have to do is LOOK at a BT, its size and composition, to see what it is. It's a mid-sized entity which was once a thetan, and its connection to divinity is lost. That can happen to a thetan. That connection is the difference between a thetan and an entity. Hubbard calling these things "body thetans" is a slight misnomer because they are ex-thetans (ex-divine) attached to the body. In magickal terms, a BT is vampiric because it survives (persists? lol) by sitting in the energy field of a body. Without constant renewal of an energy field, an entity will fall apart in a short time.
There are many different types of beings. Hubbard didn't catalog them. (I probably should sit down and write down the types I know.) Hubbard probably didn't catalog them because he didn't know them. There's a helluva lot Hubbard didn't know . . .
It's been thirty five years since I've looked at it but, as I recall, it ranges from beings who are classified as AAA, then AA, the A, then, B, then C, then D, then E Targs, then, I think, Genetic Entities. Link to The Akashic Book of Truth
Filbert wanted people to believe that Scientology tech was derived from the cosmic Akashic records. Ref: Hubbard's experience while under nitrous oxide at the dentist's office in 1938.
Anyone curious about this will have to go hunting for this themselves. I don't recall where it was in the book. (If someone finds it, feel free to post it here.) Who knows? It may draw Haiqu back from the Main Body of Theta, or some such.
There's also a chapter in the book Messiah or Madman? titled Are You Haunted? that addresses this general topic.