Flows logically. I also forgot that the summoning rituals were taught to the beast tribes by the Ascians only after Silvertear, though as it's possible to summon without their ritual it could simply be assurance that primals summoned from then on would have behavioral patterns that align more closely with their goals. Easier summoning conditions would provide a golden opportunity they'd never pass up as well (assuming it wasn't of their own making).
That... still leaves Mysterious Primal X, summoned during the conquest of Ala Mhigo, unaccounted for though... I think. Ala Mhigo was conquered before Silvertear, that much is certain, and a primal was reportedly summoned in the region as a consequence.