There is a lot of anecdotal evidence with mares and cows having their babies together! In fact I had 2 mares foal within 30 minutes of each other once!
And then one need only look at wildebeest and antelope in Africa, and caribou in the arctic who all drop their babies within a week or so so that they all are growing up together.
I don't see it as any stretch that pullets would also be affected by such things. And isn't it said that leaving chicks in the incubator will encourage other chicks to hatch with their cheeping