Yesterday, while perusing my old AD&D Monster Manual II, I was looking at the index and found some intriguing demon names that, as far as I know, never actually got used or statted up. If you look at your old AD&D Monster Manual one, under "Demon", note what it says for Type IV, V, and VI demons: "Nalfeshnee, etc." "Marilith, etc. "Balor, etc." Well, in the index to Monster Manual II, they give names for additional demons of those types: Type IV includes Nalfeshnee AND Bilwhr and Johud. Type V includes Marilith AND Aishapra and Kevokulli and Rehnaremme. Type VI includes Balor AND Alzoll, Errtu, Ndulu, Ter-Soth, and Wendonai.
This raises a question. Are each of these names those of an entire type of demon (my guess), or were they supposed to be the names of individuals? If the latter, it would imply that the authors meant there were only six type VI demons in existence, which is barmy. (On the other hand, it was once suggested that there were only twenty-four balors in the Abyss, lol!) On this theory, there was once a demon with the personal name "Balor", another named "Alzoll", and so forth, and the entire breed of balors are named after the original. Which makes one wonder what happened to his five brethren?