We do not know it hasn’t happened. The fact that both the Night Elves and Trolls have legends of the Night Warrior gives credence to it have happening before.
We found three Night Warriors in Ardenweald, Maldraxxus, and Revendreth, however that does not mean there aren’t more out in the Shadowlands. In the alpha there was even a Night Warrior set for Bastion:
- The Path of Totality - Retrace the memories of Caregiver Selenis and her path to becoming a Night Warrior.
Caregiver Selenis made it into the game, but she’s just happily taking care of Stewards, her memories of life purged by the Kyrians like all others before we made Adrestes the new Paragon.
Exploring Kalimdor was also written by Sean Copeland, Blizzard’s lore historian, who has stated he doesn’t hold Blizzard’s creative developers to having to adhere to previous lore, so if the Night Warrior established the Kaldorei Empire is what Sean Copeland is going with then that will have overwritten the history to be the case now.
- “My team believes that continuity exists to enhance a story, not to tie the hands of creators,” says Copeland.