I have 4 hens that were hatched this spring that are going through a partial molt. Its fine. They are 8 and 10 months now.
Now my older hens DROPPED a lot of feathers all at one time. Its a more drastic quick drop than the pullets.
I would only be concerned if the feathers start growing back and then disappear........like another hen pulled them out. I did have to keep one of my older hens that dropped all those feathers so fast, separated for a couple of days because I saw a few scabs on her shoulders. I think the other hens were just over doing it with "helping" her get her feathers fixed up. If you start seeing any scabs of blood, that is when I would be concerned and maybe keep her separate for a bit so they can grow in at least enough to cover her bare skin.
Since they started their molt, my Amercaunas have roosted in the spare coop. They don't want to be with the others right now. I respect that. Probably got picked on. One of my Black Stars always has a harder molt. Her comb turns pale and she hides. I've been giving her mealworms everyday and she seems a little perkier. But still doesn't come for treats, I have to go to her. But she's eating ok, just hiding out.
BTW, I forgot, how long to get grown out again? I think they are close to being finished dropping. Funny thing, remember when Prim had that sour crop recently? The others were already well into molt, but Prim didn't start her molt until she was well and I took her out of sick bay and put her back in the coop. The next morning the coop was full of red feathers.