The game's progression always had a pattern to follow. Da Fei took out all the Mages in the newly built Magic Watchtower, so the old watchtowers had to pull people out to fill the vacancies, leaving the old watchtowers understaffed. Thus, the disguised Deirdre naturally blended in. As for how Deirdre, after infiltrating, would relay the intelligence, this question didn't need to be tangled with, because this was a game, not scientific research; what the NPCs said was what it was.
What did it mean once you controlled a powerful old watchtower? Of course, it meant blasting everything around, especially that row of broken ships by the shore! Once they were cleared, it was time to skedaddle. Da Fei made a decisive decision, and the sneaking operation commenced again!