When the seller is selling an over wintered nuc, I don't want to see empty queen cages laying about. Would you want an over wintered nuc with this year's southern queen? We're talking the first half of May in the north east.
In our part of the world, spring nucs are sold as 4 frames units. If I was going to make nucs from a colony, here is how I would do it. I start by walking out to the double deep wintered colony carrying 2 4 frame boxes. I pick thru the frames of the wintered colony, each of the boxes gets 3 frames with brood, one with pollen / honey. Bees are shaken into the bottom box off of all the frames except the one with the queen. Frame with queen goes into one of the two 4 frame boxes. Now excluder goes on top of the deep left in place with all the bees, and the two 4 frames go above the excluder. Lid over those.
Come back the next day with two caged queens. Take two nucs off the top, one is wintered queen with bees that are her offspring, and brood in all stages, pretty much the definition of a wintered nuc. The other 4 frame box has brood in all stages, gets one of the caged queens. The bottom box now gets the other caged queen.
Net result, one wintered nuc to sell, one spring nuc to sell, and the leftover bees in a box with a queen, they can build up a colony over the summer to do it all again next spring. In a couple more days the queens will be out of the cages, we go thru pulling out empty cages and confirm there are eggs. At that point, nucs are ready to go. If we were rushed when pulling cages, you may well see a couple empty queen cages in the grass, but they will end up in a pocket or bucket by the end of the day.