toxic wave
During one of the early Smuggler quests to check on a lost ship said ship seemed to have unlimited Blackbeard Crew respawns. This happened multiple times after multiple restarts and re-returns to the ship in question. Regardless of whether we had the quest active, whether we boarded the ship or not, and regardless of how many enemies we killed.
Not sure if it was supposed to be enemy pirates or drowned, but the ships with drowned enemies didn't have the same respawning problems. Perhaps that ship was flagged as a Blackbeard ship instead? When not aggro'ed the enemy crew acted as if they were sailing the derelict ship.