You're right, I was confused on the dates. I'm not referring to the sealed envelopes, but rather to the practice by which an alchemist/scientist/mathematician/etc would write a succinct summary of their discovery (i.e. "to transmute gold, add salt") and write the letters in alphabetical order. They'd publish this somewhere public. Then, if someone else discovered the same thing, they would say "aha, but here's my discovery" and point out how they came up with it ten years earlier by giving the "unhashed" version.