My 21 week RIR's finally started laying. I have no way of telling which of the four are laying which eggs. First 4 or 5 eggs were hard shelled, next three were soft, rubbery shelled. All hens supposedly hatched on same date, but a couple appear to be more immature than the others. Will a less mature hen lay a soft shell egg as its first or will any hen for that matter lay first a soft shelled egg? I am adding oyster, shell to their feed. Any advice would be appreciated.