I would say the greater the numbers, the greater the odds.
I don't believe anyone thinks the Lusby's are breeding for AHB traits in their efforts to battle the mites. What concerns some of us is that, it is working because of the AHB genetics, regardless of how they got there. The evidence presented by M. Bush, yourself, and others seems to indicate that the genetics may not be as large a factor. I hope you are right. I have recently read that in some instances, colony collapse has taken up to 4 years from initial infestation.
The mechanics of viral spread within the hive is something I have little knowledge of, are mites the only delivery system for the virus? I would think that once the virus becomes active in one bee, that single bee might carry a viral load capable of decimating many colonies. Again, I don't know the mechanics, so the length of a beeâ€™s life, the caste and tasks it performs, the rate of reproduction within the colony, would all influence the time necessary for the virus to become virulent throughout. This would seem to be supported somewhat by the number of colonies that fail in winter when brood rearing slows or stops and population begins dwindleing.
As I said, I'm trying half my starts this year on small cell. It really hurts to think of retarding those colonys drawing comb when I(they) worked so hard getting those extra deeps drawn last year. Oh well. TIme will tell.