A couple questions from a first year keeper.

So I did a regular general inspection yesterday and everything looked pretty good. I didn’t spot the queen but did see newly laid eggs and larvae in various stages of development plus a few in the process of hatching. There was some capped brood along with some capped honey etc. I noticed something I thought strange with some of the Oldest brood cells though. Rather than the queen reusing some of the oldest brood cells, it appears they are being filled with nectar/honey. Is this normal for brood cells to be converted to honey storage??? My hive is a captured feral swarm so it is only a single deep brood box. Does this brood to honey cell conversion mean that I need to add a super or another brood box even though there’s still 2-3 untouched frames in the current box???