For the Japanese cards, there are Android apps that can read the last several transactions using the phone's NFC chip, so there's obviously local storage there

For the Japanese cards, there are Android apps that can read the last several transactions using the phone's NFC chip, so there's obviously local storage there too. Although my guess is there's redundancy with online data to ensure there's no shenanigans. The cards also work on other things, like the many vending machines in Japan, I wonder if they're all online. Maybe the protocol is designed that subtractions are easy but additions are hard...