Ok, you win. Extra points for mentioning DEC and not that gawdawful VMS. In the 80s I did some coding on a pdp-11 running BSD and loved it. But anything on VMS was a chore. I know people who still suffer with that even today because companies refuse to update their workflows. Meanwhile the vax hardware no longer exists so it's running on a virtual machine on a windows blade server. Crazy.

Anyhow, I always called em demons when I wrote em. But I'm dyslexic so spellings not my strong suit. I actually only noticed people using the extra A maybe a decade ago, so i figured it was more history modification like the backronym you mentioned, or possibly some British spelling affectation. :)