> You could prove that an event happened before a certain timepoint (not after it). Not with what GP proposes. If I understand their proposal correctly, it is

> You could prove that an event happened before a certain timepoint (not after it). Not with what GP proposes. If I understand their proposal correctly, it is to include a value from "the current-highest-block from a blockchain to incorporate proof of a previously-unknowable, globally-verifiable value." You can always include historic values trivially. It is much more involved to actually do a transaction on that chain, which could indeed be used to prove existence before a certain time. But yes, your alternative proposal would work for that, if you assume the chain cannot be controlled by any individual/partisan party.