After too many years, a dishing tool was acquired. The subject wheel was dished as it should be. Much confidence was had in placing the wheel on the bike.
It looks like the rear triangle is off by 2mm.
This may have been a result of a couple of crashes or the bike was never aligned. I don't know. I don't think the offset was significant enough to really sense it while riding, especially if the the disk put the wheel in the center.
What are your recommendations? Dish the wheel or tweak the rear triangle? The engineer in me says to tweak the frame by locking in the DO and gently applying force to the DO leveraging near the BB and seat cluster lugs.