Fascinating! Why didn't I think of that ...
Update ~ So Apis, the queen has been MIA since yesterday morning. I waited until this evening to keep checking for her. Yesterday the bees, without the queen, were very busy and excitable, not aggressive or even insistant, even went in the nuc with no veil. Today, they are their normal busy selves but still no queen.
This queen was not very plump, but I've had slender queens do just fine. Is it possible, that this queen was not fully mated when she came to my house 11 days ago? Could she be on a second mating flight?