I had a similar experience last fall and winter. Lost 3 strong second year hives in the fall and the remaining 8 over the winter. All second year hives superceeded in late September. I monitored for mites and really didn't feel I had an issue, but the only treatment I have done is powdered sugar. This early spring I sent samples from the 8 hives to the USDA for mite and nosema testing. I also sent an aggregate sample to BVS for virus testing. The only thing that came back positive was varroa. Some 50 bee samples had 7 mites. The USDA says 5 mites per 100 is a hive that is in need of treating. The only thing I can surmise, is the early spring we had last year gave them quite a few extra breeding cycles.
So I have repackaged 4 of the hives this spring and other than small queens, they are all doing well.
In the early spring, some feral bees were coming around and very reluctant to enter the hives. Now the packages are robbing the other 7 hives.
So, your situation sounds like mine and possibly your hives are still worth some money. Are they being robbed out? One sign of CCD is the reluctance of bees to rob out CCD infected hives.