Game Mechanics: NPCs casting spells that they shouldn't until a certain era

[Rygar]

Nilbog, I started compiling a list but wonder how to flag the original example (i.e. Grim Aura). For instance, Grim Aura is a 'Classic' spell for a Necromancer, but a Shadowknight only gets that spell in 'Velious'.

So how should that spell be categorized, do you need to add classes to the era tag? Such as:

346    Grim Aura    Velious(Shadow Knight)
or
346    Grim Aura    Classic(Necromancer)     Velious(Shadow Knight)
or
?

I'm not sure how many other cases of this there are, but that one just jumped out at me.