Smaller colonies can starve to death easily in very cold weather with ample honey stores. The size of a cluster means a lot in the winter. The larger clusters can reach far and wide to gather honey. Smaller clusters will consume the honey around the cluster and when it stays cold for so long they just can’t move to the honey.
If you open the dead out hive and there are bees in a cluster clinging and they r buried up in each cell they r stuffed in there trying to gather nectar and stay warm and they simply starve from being unable to move to the honey it is a common fate and no ones fault it just happens with late swarms which do not reach a decent size.
With late swarms and not knowing the age of a queen if you can raise a new queen by August she will be a vibrant fall layer. Take any extra combs of honey and put directly above the center of smaller clusters. If you have any flight days in late winter check their positions in relation to the stored honey and move honey if need closer to the cluster.
Another thing is keep a couple young queens in Nuc boxes all season for late swarms and weaker hives. Combine them into larger stronger hives in the early fall.