No Queen in the New Hive

I checked yesterday to see if the presumptive new queen was busy laying.  I found two frames full of bees on both sides.  The bees had been filling cells with nectar, which they were busily gulping down thanks to the smoke.

Both queen cells, which had been capped, were empty but there was no sign anywhere of a queen.  Am I wrong in thinking that it they should be done with mating flights by now, at least a week since they emerged from their cells?  Did they both succumb in a fight?  Did the remaining queen fail to survive her mating flights?  Another question came to mind.  The bees will try to make a queen if they discover they are queenless if available young brood is present.  Are they always successful in determining if the larva is sufficiently young enough to be a viable queen candidate?  In other words, can they go through the process of continuing with the royal jelly,  constructing the queen cell and capping that only to have an ordinary worker bee emerge at the end?  I have no idea, and perhaps someone knows this answer.
At any rate, I added a couple more frames.  There was definitely some very young brood in at least one of the frames, so we'll see if this one works. 
I decided to go ahead and look in both of the other hives since the smoker was going.  Those queens have been laying like crazy.  There were many frames very full of brood.  They have also been putting in a lot of honey in hive #2, which is good since they had come out of winter pretty light.  Much is already capped.  I did not check the super I had put on that hive last week but I'm feeling, with the clover going strong, that I had better add a second.  They can at least build out comb on that one.  Hive #1 also had a ton of capped brood and was looking to start growing quickly in numbers.