. . . these were items used during the development of the game and not removed from the data files when the game was marketed.
About 15 years ago, I read through the data files (using a hex editor, I think), and I found all sorts of stuff in there. The only one that is still partially in my memory was a named sword (although I can't remember the name) which I thought might be quite tasty. However, when I activated it in a throw-away game, I was disappointed to find that it was a very ordinary +2 sword. I suspect that somebody else did as I did and just listed what he/she found, and the lists you found were the result.