The fact of the matter is that chicken sexers aren't perfect. The last I heard from the show "Dirty Jobs" who went to Murray McMurray to watch them sex chicks, it was stated that they are about 84% accurate in sexing. Even when you go into the feed stores, you will see that the "pullet" bins have cockerels in them, if you know what to look for.As one of my daughter's was holding one of the new chicks, she looked up at me and said, "Dad, could any of these be roosters?" I responded with, "Well, there is that chance." What has me worried is I asked myself that same question when I picked up the chicks from the coop. I hope we haven't jinked ourselves. LOL.