As far as i know (well i know this for truth with some seedbanks - but it may not be how all of them do it) seedbanks take 100% females, and apply a chemical to them so they create male flowers, then use the pollen of these to pollinate the other females, this produces seeds which are a very high percentage female. These can however still turn out to be male (very low percentage) or hermaphrodites, its usually down to stressing the plant if it turns out to be hermie though as far as i know.
Also as far as i know feminised plants pollinated do not create feminised seeds (unless done correctly by the above method or others that are probably out there - i hear using pollen from a hermie on the same plant usually creates female seeds, the method above though is
not actually a hermie)
Hope this helps and am willing to defer to some1 more knowledgable than i
