To recap: the single original hive had larvae both above and below the queen excluder, so I moved half the frames into a new hive, and (re)placed queen excluders on top of both. The aim was to split the original confused colony into two hives, and hope that the bees would re-queen as necessary.
Well ... it seems to have worked. I now have two thriving colonies. And yet bizarrely, I could find absolutely no trace of brood in either hive.
After a full hive inspection - right down to the bottom board and looking at every frame - I saw no larvae. No drone cells. No queen cells. Yet the bees are very busy, and I even took four frames of honey out of each hive.
What on earth is going on? Now I am *utterly* baffled.