I've been contemplating posting this all year. I am not dictating or disparaging anyone or their ways. However I wanted to throw this out there as my experience has been much different then the norm and perhaps this will help some having the same issues.
Been doing this 5 years now. From the beginning i chose to use OAV to treat mites for the price point. I always treated spring and fall when mostly broodless as well as twice during the season (four treatments 5-6 days apart). This along with mite washes took a considerable effort to accomplish. As my hive numbers grew i'd be spending hours just doing OAV. I still was having horrible overwintering numbers. anywhere from 50 percent down to zero overall. So last year I used one treatment of MAQ's in august for 2 weeks. I did not use OAV at all last year.
Second thing I did was not close the entrance at all. I have metal mouse excluders and normally i tape them partially closed so there is only about a 3 inch opening at the bottom. I use quiltboxes with a top entrance drilled into it. Not sure how much this helped but figured i'd list all i changed and the results.
I try to approach problems by changing variables. By changing these two things I got about 90 percent success with overwintering. Still lost a few that looked promising but I will definitely be sticking with this recipe. One season is not a proven concept but the changes are amazing. Perhaps there are some new keepers trying to decide that this might help.