My guess is you are more the exception than the rule when it comes to frostbite. I wish we were all this lucky.
It is extremely frustrating when you think you have researched to the ends of this website and back again and this sort of thing brings you to your knees in such a humbling fashion that it resets your gears. You learn there are things you just have to accept that are out of your control and you just maintain what you can and learn to "let go". --very difficult for me sometimes. The biggest lesson for me was the "letting go" part and picking the breed part when it comes to this. I will always practice good husbandry with my birds--so don't get me wrong on the "letting go" part-- but there are somethings I've learned is that everybody's advice is different and that is because they have different birds, they have different number of birds, they have different climates, they have different coops, they have different bedding,.....etc etc. etc. And always watch your own birds and see what is happening to them and take all of this advice with a grain of salt and incorporate only what you think is going to work. Last year I thought, "I am not going to have weak, unwinterized chickens."--no heat, no insulation. This year I'm thinking: "When it's -30 I'm warming that coop up and insulating with snow and foam boards on the north and west sides so it is not a cruel temperature (0 and above I'm okay with )." Funny what a year does to you.