Queen prisoner

I inspected some of my hives yesterday evening and noticed some sealed swarm cells that have been in place(have been sealed) for two or more weeks. Out of curiosity I decided to crack one open! To my surprise these cell contained living queens. The queens appeared healthy so I used them in nucs. After closer inspection I relized these cells had been reinforced to prevent the queens from emerging. I have read about this, but after looking back cannot find any detailed info on the matter. So.....here come the questions:
Why would these queens be held captive for so long?

Are these cells opened by workers and the queens fed and then locked back up?

Are these still good queens (if they survive mating flight)?

Also...A few of these captive queen were dead (already slimy) Why would the workers not remove these cells?