Quote Originally Posted by TheMightyMollusk View Post
Summoning a primal requires an honest belief in the being one is trying to summon. The Archbishop knew the truth about the original King Thordan. He knew that the King abandoned his crown after the murder of Ratatoskr and the theft of Nidhogg's eyes. He can't have intended to summon the original, because he knew that the popular image of King Thordan was a lie.

The Knights are a weird case, because we see three of them transform into their primal forms in the Vault (and a fourth afterwards, when he kills Haurchefant), quite a while before the fight in Azys Lla. Whatever they were doing, either it wasn't tied to Thordan to begin with and he just empowered them, or they had summoned Thordan earlier and gained their own transformations, but wanted the power in Azys Lla to make Thordan even stronger. If the latter is the case, then it's entirely possible that Archbishop Thordan was tempered before we ever even met him. But, see above.
We can see from Satasha (Hard) that primals can grant their tempered subjects new powers and transformations, so I just assume that's the case with the Knights of the Round.