Well I'm the numpty now. I finally loaded up the spells data for P99 and the correct values are already in the spells file.
I guess I'll just ask a necro to tell me how much hp he's losing per tick in CoB / Lich and we'll see if that's as expected, and then if so we can resolve this.
(I'll just check next time...
[You must be logged in to view images. Log in or Register.] I'm allowed a stinker bug every now and then, right?)