I'm saying that you can have a flock of 1 year old hens that have never seen a rooster in their life, crack open an egg, and it have a bullseye. That's all I'm saying. So it can't be super accurate if me (who only has one chicken) and Odd (who only has hens), OP (who only posted pics of females)...
Another good way to tell is by the fact you only have females? and have had them together without a male for longer than 2 weeks. That would mean they are infertile.