you probably have a hermie plant or two that you have missed and pollenated the other plants in your grow room.
pollen has a very short life span and it wouldnt be viable from one grow to the next.
seeds from hermi plants will germinate fine but be more likely to turn hermi sometime during your grow I personaly wouldnt use those seeds, if you want a seedless crop you may have to purchase some seeds, and would stay away from feminised seeds and nirvana to increase your chances of getting good stable genetics.