The word locally (central NY) is that supersedure was remarkably common
this year, for some strange reason.  I had a few colonies which were doing
great, building up with first-season queens (some reared, some bought),
only to find the queen GONE after filling the hive with a beautiful brood
pattern.  Supersedure/emergency queen cells would be scattered through nice
solid patches of sealed brood.  However, no eggs or young larvae. No
swarming involved, either.
I mentioned this to a friend running abt 200 colonies up north of here and
he mentioned that he and others had been seeing much the same thing.  Could
this be more than coincidence?  Possibly related to the Apistan...?  Hmm.