That's why I said "unlimited supply", not just recycling their own. My hens don't lay in the winter so I buy eggs, and save the shells. This makes up for any deficit over time from only feeding their own. So if you do offer and unlimited supply (as in, eggshells are always available and don't run out), then no, they don't need oyster shell or anything else.Recycling egg shell back to the hens isn't enough for them, they need to have oyster shell out there too.
Mary