I don't have nearly the experience or knowledge as many people on here as far as breeding. This point has been touched on but I don't think it has been emphasized enough. Something I've learned with my little backyard project is that you need to be able and willing to hatch out a lot of chickens and raise them to a point that you can make a rational decision on which ones to keep. I only hatch enough for the two of us to eat. Except for injury or disease, I don't cull, kill, or in any way dispose of any chicks until they are eating size. Even with my limited goals it is hard to improve my flock with those few chickens to choose from.
I can't imagine how many you would have to hatch to get them to conform to the SOP and then keep them there. As someone mentioned, just a couple of generations of bad breeders and you have lost everything you have gained. To be able to choose good breeders you need a lot to choose from.