I can see through the observation window that the swarm that I reported a week ago is clustered and building comb.
The hive that threw the swarm started from a late swarm last year. It had been hived in two Warré boxes, but had only filled one of them, the lower box being empty. Today I checked this hive. I tipped the occupied box first on its side and then upside down (keeping the combs vertical in the plane of rotation) and had a good look at the bottoms of the combs. I expected to see several queen cells. Despite having a clear view up between the combs (a good portion of the bees having left with the swarm), I saw only two queen cells, both capped and at or near the bottom of two adjacent combs. One of the queen cells was completely perfect, like the pictures one sees in the books. The other was less so, but still passable to a non-bee such as myself. However, clearly it, or its occupant, was not passable to the bees, as the side of this queen cell had been torn open and it was empty. The bees had chosen which queen they wanted. I expect the remaining queen to emerge from her cell in the next few days.
So much for the idea that swarming bees always make a multitude of queen cells. This hive appears only to have made two.