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Luria Nova recently TOed some regions, among them Aveston. With 725 peasants out of 8300 possible, almost starving, at 'Stopped' production with no knights nor lord, it produced 488 gold for the Duke. A little too good to be true, right?
The first tax. That's gold that had accumulated over a potentially large period of time. Happens sometimes with regions just TOed, especially on Dwilight.
If the region was rogue, who the hell would have collected those taxes? Apparently the "minor nobility" that was there didn't do a very good job (minimal production), so I don't think they would. And if they would have done so, they would certainly not have kept all that gold stored, ready to be picked up by a realm that seizes power in their region.