Hi Peter,
Your query sent me off on an afternoon long search for answers on the web.
Nada, zip, zilch as an answer to your primary question. 
I read a lot about qPCR testing though; and viral RNA titres and sampling techniques and mite piercing, and what is detectable, etc. Higher cT number is better, but how much better? Totally agree that there should be some indication to you, the client, on what cT levels indicate danger, on a virus to virus basis. 10,000 virus detected per bee might be good, might be bad. How do we know? 
Beyond that, what can you do about it? No Varroa, so no vector? What anti-viral would be available to a beekeeper?
We treat for Varroa and rely on nutrition and the bees to do the rest. I'm not sure what you would do with the cT danger level information.
Best regards,
Brian

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