It could simply be genetics and not grower error, new seeds I always grow out in 1 gal pots and clone them beforehand, so if they fail I will just toss their clone out and throw the whole root ball and plant into a contractor bag. If they succeed I have a noted clone of it, and I can reproduce the success.
I have made the same mistake of putting lots of care and time into new genetics, usually seeds, putting them in a large container of grow medium just to have to throw it away a couple months later due to herm. Running a bunch of smaller plants and moving them to flower ASAP to see how they perform or if they hermie is ideal practice in my situation.
p.s I've had plants that show female until like 2-5 weeks into 12/12 and I know the feeling, it's plain devastating. I will tell you, those plants need to be trashed and you need to wipe down the tent using some type of sanitizer spray to kill any potential pollen that might seed new females. Don't believe the myth that water kills pollen, if that was true there would be no seeds in nature.