Thanks for reaching out with this question. Adult honey bee workers experience temporal polytheism, which means their work/roles change as they age. 

Worker honey bees also respond to the colony's needs. If younger workers are absent from the hive, then older bees revert to roles of younger bees. If older workers are absent, then younger bees will begin foraging at a younger age (precocious foraging).

It's common for beekeepers to give frames of brood to queenless hives to allow them to raise a new queen. The frames of brood you gave the queenless hive may also provide younger generations of worker bees.

Happy beekeeping!