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Nah, not really.
"Izra and Vidomina, who gained the Expert Spellcasting skill through a method different from the one specified in section 5.10.2..."
Izra and Vidomina, who escaped from prison, gained Expert Spellcasting through a method different from the one specified in section 5.10.2.
That is, strictly following the RULES, they cannot be used.
And I insist that it's not a given that allowing them to be used in this situation is self-evident (although I personally understand the idea behind the rules, that they can be used), but the fact remains that it's much easier to free an overpowered hero from prison than to develop them independently!
And the purpose of the rule was to limit this overpoweredness. Another question is what exactly they meant.
And since I myself am a fan of the Warlord mode, where necromancy is completely disabled, I am not really capable of understanding these nuances. This rule is a workaround. No matter how you phrase it, it's still a clumsy workaround. It's impossible to understand anything based on common sense here (think about it - in Warlord mode, with necromancy disabled, the undead faction still consistently remains in the top 3, and with necromancy enabled in the SoD expansion, I've seen players simply switch to necromancer heroes).
Common sense has not yet prevailed in this rule, so it simply needs to be reformulated to avoid ambiguity.