i missed a bird once that was a double beard. i know that because 2 days later my buddy and i went back and doubled on the one i missed and his buddy.
my opinion on multibeards is simple. there are pockets of birds every where that have a bunch of multi bearded birds. but multi beards can show up anywhere at any time. kind of like bearded hens or non typical bicks. some places have more than others but they show up from time to time all over.