I saw that Mike Rowe episode. They were vent sexing. Season 1, episode 7. They seemed to like squeezing the poop out of the vent so they could see inside the vent. You don't need to squeeze the poop out to feather sex. You may want to watch that episode again.
They do use feather sexing...
We all have different flocks. They are set up differently. The science says you cannot count on feather sexing (or any sex linked sexing) unless you know how the parents are set up genetically. I don't know how yours is set up. It is possible that purely by accident yours is set up correctly...
This thread talks about how to sex chicks by certain characteristics. Typically these characteristics show up around 5 weeks. On very rare occasions I've been able to sex a chick pretty much at hatch, posture can make it obvious. But that is really rare. I've had some reach 16 weeks before I...