I understand the differences between brood and honey cells and drone and worker cells, but wondered how it worked later in the season when the queen throttled back brood production. Are old brood cells used to store honey and pollen, or are they just left empty until Spring?
The bees back fill it with honey as the brood emerge.
Usually the brood nest gets some nectar in it to shut down the queen. This is usually cleared out when they start clustering for winter. They need empty cells to cluster properly. But a lot of the edges will be filled and capped. The bottom box often has a lot of pollen stored in it.