That is what I would have expected to happen, not issued with cracks already in the helmet as the listing suggests.
At the manufacturing stage forming the helmet bowl out of the special high carbon alloy steel, without it cracking, is much tougher than if the same operation was carried out with a lower carbon mild steel. I don't know that the US ever heat treated their M1helmets during the manufacturing process but it would be logical to do so to achieve a consistent level of hardness.