His conclusions after reading his White Dwarf.....
Chaos Daemons (40k)- Phil Kelly
Daemons of Chaos (Fantasy)- Matt Ward
Here is his email, and hopefully we get something a little more concrete in the next day or so.
via the Faeit 212 inbox
I saw some people in the responses wondering about authors. I have the White Dwarf in front of me and Phil Kelly is mentioned as the designer of the Codex, and it isn’t explicitly stated but it seems like Mat Ward is the author of the Fantasy Army Book(there is a section in the back talking about a map that’s included, and that Mat took “a lot of inspiration from Liber Malefic.”