Regardless of whether you are using two deep bodies or three medium bodies for wintering colonies, in either case, the UPPER half of the colony was all capped honey in November, and the lower area was some brood, some capped honey, and the CLUSTER of bees. As the winter progressed, the cluster slowly moved ALWAYS UPWARD (never sideways) and by February the cluster should be in the upper box and leaving the BOTTOM HIVE BODY TOTALLY EMPTY OF ANY THING.
Brood rearing is well underway, honey stores being rapidly used, dandelion nectar is about to appear, pollen is available, winter bees are dying, young bees are becoming VERY numerous, and the IMPORTANT thing for the bee is NOT honey, but BROOD rearing! In spite of all that empty cell space in the EMPTY bottom brood box, bees just REFUSE to go DOWN during those chilly months, but if they run out of queen laying space in that upper brood box, they will SWARM (and probably die of starvation); Science has NOT YET deciphered why the bees will NOT go DOWN in the early spring, but swarm instead. YOU, the beekeeper, could have easily prevented this swarm by simply REVERSING the two brood boxes, so the box with all the brood, queen, and the bees are now in the BOTTOM box position and the former EMPTY bottom box is now in the TOP box position, and NOW the queen can move UP and have LOTS of SPACE for laying eggs.
YOU only have to provide 1:1 sugar syrup through the inner cover hole to provide lots of food to the bees who are making their brood nest just under that inner cover hole! I have just described maybe the most important anti-swarming technique called REVERSING. Some lazy beekeepers have just added another empty brood box on top of the existing boxes rather than REVERSE. History has shown that this is harmful because it just increases the box volume that bee cluster heat has to warm up; so REVERSE! Now, I hope you know the proper definition of “SPACE”.