One of my triple boxes which had 30 frames full of honey still has 22 frames full of honey and they died right in the center top box.
If they had reserves, no nosema, afb, mites etc.. and they STILL died, then I honestly believe this was NOT something that was your fault. I do believe it is the fault of the genetic line of bees you are trying to winter.
Time and time again I have had the argument with folks that tell me that ANY BEE can overwitner ANYWHERE if it is done correctly...
Unfortunately, they do not go into detail about the hive heaters they use, the dehumidifiers and custom insulation while ranting that I am doing something wrong...
Personal experience has shown that such statements are total bunk.. the type of bees you have DOES very much matter.
If you cant winter the bees you have, using PROVEN methods, get better bees!
I had 4 hives of local bees go through the winter this year with NO wrap. Just the insulation on top to stop condensation, and the sugar cakes in case they needed them.. all four hives are still alive.
The hives I lost were packages and daughter queens from the package bees.. as of today, every one of the 20 locally bred hives I owned is still alive and flying.
Try it yourself! Get some new bees, and put locally bred PROVEN queens in those hives when they are going well. You will be amazed at how well they winter.