The mint guardians can publish the addresses where they hold btc, so that can be verified, but only the guardians know how much ecash they have issued. So you can't verify liabilities to check against reserves.

With liquid, you can see the addresses where they hold the btc that has pegged-in, and I'm pretty sure you can run the equivalent of gettxoutsetinfo on a liquid node to verify how many coins have been created (didn't actually look this up, just remember reading it somewhere).