We changed the way we went into the winter this year. Last year we lost almost 50% of our hives which was the local average.
In the past we had never treated for Varroa Mites ~ this year we did. The highest causes of winter losses has been attributed to Varroa. We also made sure all of the hives were heavy with honey and had a good amount of bees going into the winter. We did combine a few weak hives with strong ones in the fall and will do splits in the spring ~ if it ever gets here.
I have been totally chemical and treatment free for the last nine years, it was a battle the first four years but now I don't even think about mites and enjoy about five percent winter losses. I believe that strong hives with good stores are the key to overwintering and like you did, combine the weak in the fall.