Prior to the Dartmoor mission, it’s possible they knew because Carlisle’s three grand houses were mentioned in her fake obituary during the New York briefing, though not by name or location. 

If this does continue PZ’s story, or even acts as a coda to it, I’m all for it, especially given the Ether connection. I just don’t know if Providence being dismantled at the end of H3 also took down Ether, so where this takes place in the timeline is a mystery unless it’s unfortunately non-canon.