Old staling data may be useful, by the way, to see whether the problem is chronic. And that's the main reason to know who stales: to see whether you should look for replacement before it's too late.
To Septimius on potential teams:
While it's surely possible for old enemies to ally (just look at European history of last centuries!
), it's still rare. And what I consider beautiful in Dominions nations is that there are almost never clearly Good ones (maybe MA Tien Chi. Maybe.), especially if we look up all 3 eras. And nations change in their outlook over time. Hinnom is clearly evil, but Ashdod less so. EA Ermor isn't (so) evil, but LA...
C'tis isn't evil
per se, but Miasma makes it looking quite like it in MA. Abyssia becomes more evil over time. And so on. And in LA usage of Death and Blood magic doesn't make nation evil in and of itself: almost all practice one or the other... So while I agree with your idea of Heaven/Earth/Underworld teams, I suggest mixing them more by lines of traditional alliances and enmities.