I can confirm it happened before Reaper's Due. My pre-RD game had Pisa conquer the entirety of the De Jure Kingdom of Africa, while Aragorn has Algeria, and France owns half of Spain despite not even owning Aquitaine. Pisa eventually lost its coastal territories in an absolutely huge revolt (despite being no friend of Pisa's, I was actually going to help them out and land troops there, but I stopped when I saw a 20k rebel deathstack sieging their last African province). Funnily enough, apparently the Pisans had been adept proselytizers, so Kingdom spawned by the African Revolt was, in fact, a Catholic country. I strongly preferred that to a powerful Pisa, so is good for me. They are strong enough that, they've survived a couple Jihads (they are helped by the fact that the Knights Hospitaller control Jerusalem and draw some of the fire), and even Holy Warred for some tiny province in Sicily the Sultan of Egypt snatched up.