Quick visit today to check that the queen is Down Below, by looking for new brood.
The good news is that Yes, there are definitely new larvae below the queen excluder, in the frames of the super that I am using as a half-brood.
Unfortunately, this super now being used in the brood area is the one I moved down at the previous visit. Put another way, there may be larvae in the brood area because I put them there. For all I know, the queen is still upstairs.
In the true spirit of Incompetence, the logic only dawned on me at the instant I had finished closing up the hive.
On the other hand, the bees are filling up the supers with honey - I had to add another layer to their cake, and now have a total of four supers.