They probably do so much vent sexing on so many chicks so I could see how it was missed. I can just imagine them grabbing without even looking at them too much, then flipping over to squeeze and then sort. The spare legs could have been hidden by a large hand holding the chick. Either way, have you called Cackle? I imagine they'd like to speak with you and see some pictures. They were wonderful to work with whenever I ordered from them a couple of years ago.
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