Thanks for the congrats, I wish I could tell everyone what my secret is but.....................even I don't know. 
Last year I only lost 1 of 29, so I was not expecting a second year in a row to see that kind of success. From casual observance, it seems like good and bad years tend to alternate to some degree.
The only real thing that I can perhaps attribute it to, is vigilance. Because I don't have a "real" job 
, I have the ability (and tendency) to be hyper sensitive to what may be occurring in my yards and am able to react quickly, instead of trying to play catch up like most working folks do. I have the luxury of having the most incredibly supportive wife who allows me to do this thing that consumes me, enabling me to visit my yards on a daily basis if I so choose.
I have discovered nothing intellectually that isn't available to everyone, so smarts surely doesn't have anything to do with it. 
If I had an answer I would certainly pass it on (or at least bottle it and lucratively market it). 
I only lost ONE hive as well Perry, and my situation mirrors your own.. Makes me wonder if you havent hit the nail directly on the head. Our methods for wintering are even similar..
Most folks around here lost a large majority of their hives this winter.
I have been keeping a sort of unscientific tally of hives.. total and lost...
Currently, of 633 hives cared for by members of four different clubs where I attend meetings... 118 have survived the winter.. that is 515 hives
LOST within about an 80 mile radius around me...
That is a staggering number, at least in my mind.
Don.. NO ONE can argue that you had a 100% success rate!!!!
