User blog comment:Omega natsu2/Chapter 359: Fairies vs. Hell, Predictions./@comment-94.13.89.18-20131116204247/@comment-7418318-20131117104006

Tartarus already wiped out or absorbed all their "own" dark guilds, so attacking those that are left, would be a big waste of time and effort.

I wouldn't even count on their own subordinate guilds knowing the location of the HQ, except perhaps the guild masters and some tursted elites and I'm very sure that dark guilds not directly associated with them are unaware of their HQ's position.