>>There is much to consider here...

Can you tell us what percentage of your colonies became clinical?

>>Local bees don't you know...

I hope this is not too off topic, but if i may digress,

Local adaptation is seen and plays into the hybridization process.  Assuming
there are any unmanaged survivors in the area nearby your apiary, their
survivor genetics drift into your yards gene pool and your bees become
hybridized with them.  Over time survivor genetics become dominant as they
favor reproduction.  The inverse would be expected if there is significant presence of 
nonresistant colonies in your queen mating area, i.e. survivor traits may become diluted.

Some traits may favor some areas more than others.  For example, in my area
we have a bimodal flow.  Coming out of winter isn't much pollen or nectar
availability until mid to late January when the first maples on the sunny
slopes start blooming at the top.  From there is a gradual ramp up of forage
availability which peeks at our main flow in late April or early May.  Then
there is a waning of forage until things pretty well dry up from mid June
until our fall flow arrives in September and continues to about the first
hard freeze.

One trait that I think I am observing regarding local adaption is the
ramping up and down of brood rearing that is seen about one month prior to
the arrival of the seasonal changes in conditions and availability.

About a month prior to the summer dearth for example the colony reduces the
brood nest to a fraction of what it just was at the peak of the spring build
up, and they may shut brood production down altogether.
It's possible that this trait of brooding up and down may favor adaption
when competing in our bimodal seasonality.

Most of the successful treatment free stories are about a line of bees that
can be traced back to harvesting unmanaged colonies in the wild that had
proven themselves for a winter or two and propagating from them.  My stock
was derived from tree cut outs that were done eighteen years ago, of which
two colonies have successfully requeened themselves and have yielded 150 lbs
or more honey harvest every year since 1996.   And this has happened with
the colonies kept off treatments and not given artificial feeds.

>Typically I move the hives (150 or so) into the home yard in late fall for
winter feeding, and then back out in the early spring.  

Not all but most of the successful treatment free operations that I am aware
of are stationary.  If local adaptation involves colony operations being tied into the local flows
it's possible that that moving them may throw them off a bit unless your home yards and out yards 
are in the same area.

>>the list of questions is a bit long......  

If you haven't already consider checking out Randy's website, it's the best resource I have found that describes the rationale and methodology behind disease and pest control.

I know that there are some on the list who question whether or not natural resistance to mites and other threats is developing in a meaningful way given the relatively short history that European honey bees have had with them.  I believe I am seeing it in my area, and in my short tenure with the bees have seen how the winnowing of less resistant colonies has improved overall health in my apiary.

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