The fact that any of the embryos hatch, tells me the eggs were not frozen solid....if they would have been, then none would have hatched.Good to know! I have always heard even refrigeration for more than a few hours will affect rates. I did get a couple of live healthy chicks even from my fully frozen batch, just *also* the worst deformities I've had.
If the egg becomes frozen solid, the embryoitc cells are destroyed, ruptured, thus unable to develop.