I just answered to amlmost same question, how to rear a nuc to a good wintering hive.
The whole idea is in this, how much bees have pollen to rear brood.
One brood frame needs one frame of pollen. It comes either from fields or it comes from stores in hive combs.
I have plenty of room in my hives, because I do not use excluder. Normally bees fill the lowest box with pollen during main yield in July. All flowers are in bloom then. In august pollen harvest is difficult, because red clower is almost only plant where they get it.
Italian bee eate all pollen stores from hives and turns it to wintering bees. So it happens. carniolan saves pollen a lot to spring.
The question is, from where the hives get their pollen. You cannot rear winter bees with patty. It is not good enough to winter bees.
If you look into nucs, they are often short of pollen because they have not history. When pollen is finish, bees eate the larvae.