Some hens never lose a feather, others are barebacked by March 1st. I believe that some hens just don't hold their feathers in their skin as tightly. Some will say, "It's the rooster's favorites that are bare backed." I don't believe it. I see roosters going to town on some that hardly lose any feathers at all. You won't see as many marks on their backs either. If roosters have spurs that are long enough and sharp enough to cut or slash into the girls, look on their sides and under the wings because that is where I see them happen if they happen to get cut from them. Young roosters are stupid as rocks. They have no idea what they are doing and will grab a hen or pullet by the head and drag them around and not know enough to mount them. I have had at least one hen I know was killed by inexperience young roosters who got too rough. I went in the pen to feed them, got to the other end of the building and heard the whole flock going crazy, walked down through every pen again and found the bird I was just looking at alive, dead at my feet. I knew the roosters in there were idiots and saw how they would treat the hens before, so I am certain they broke her neck. I can't say as any others have had that happen, thank goodness.
Some roosters I never see breeding then set eggs and they are all fertile, so it has nothing to do with whether you see them.
I raise rabbits too, and I never catch a doe in the nest feeding her babies, yet, they always will have full bellies.