i think it could have been frostbite, and he took the natural path and let the dead tissuse fall off. i think you should take him into the bathroom after you take a shower when its warm and humid, and let him warm up, and put some hydrogen peroxide on it to kill the germs.
good luck!! you can do it, ok?
The damage is older. He has been inside for quite some time already.

The wounds are healing well.