While talking to some workmen during a coffee break about my hobby of photographing reptiles and amphibians one of them asked this question. How often do Tortoises shed thier shells. They don't, i replied and explained how the shell grew with the Tortoise. I don't think your right another commented ,i saw plenty of empty shells made into all sorts of things in North Africa a few years back.They must find these shells somewhere. DESPAIR.