Well I don't understand all this molting for months business. Something just can't be right. My Dels have been and done and they are back up to par. Couldn't have been more than a couple of weeks. Gradual slow down , gradual pick up, maybe a month tops. There has to be something in your feed management program if it's taking months. I don't recall reading anything that said it takes months for them to pick back up. Lord have mercy how would anyone make any money on birds that lose months of laying?
If you haven't, put them on a high protein diet to get those feather back asap. If they are not on a commercial layer they should be to kick start things. Reduce treats, chickens can fill up on junk just like us and not eat a healthy, get them to lay diet.
This takes into account that you haven't made any drastic changes in the flock or there has been no trauma to the flock. This includes a reduction of a roost mate. Even a new person around can upset them. If aunt Mazie has come to visit that can upset them cuz Lord knows she's got all them worts.
Check your feeding system, or maybe you just need some Delawares.
Wish you the best
Oh and one other thing, corn/scratch will help them generate heat for the cold nights if you live in the north. Make sure they go to bed with a full stomach.