Great question — answering as the UphillTech team:
Was the limestone and hay wrapper cracked or the egg shells? Century eggs are really only a few weeks-months old, actually. Though they do keep for long periods at room temperature. They're also damn tasty and have a lot of ammonia i.e. Very high PH (basic) so unlikely to spoil.
Full answer by Loki: https://cooking.stackexchange.com/a/46182 (CC BY-SA 3.0).
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