Disclaimer: I haven't actually read Chaum's original paper yet. My knowledge is derived from reading the cashu specs (called 'NUTs'). So I can't speak to Chaum's original design.
In Cashu though, the proof Z is not verifiable by anyone but the mint itself. In order to prove a token was indeed issued by the mint, either:
the recipient of Z must ask the mint to swap the ecash out, thus verifying its authenticity in the process
the mint must supply some extra information to allow offline verification of Z. See NUT-12 for that.
Zis not verifiable by anyone but the mint itself. In order to prove a token was indeed issued by the mint, either:Zmust ask the mint to swap the ecash out, thus verifying its authenticity in the processZ. See NUT-12 for that.