It sounds like you have no idea how credit card transactions were or are processed. They are almost exclusively file and batched once a day, even today. Back in the 1970s it was even worse because there was no real time authorization.

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He or she is correct that the cash settlements were and are batched, but authorizations, reservations etc were online - to the mainframe that's just another transaction.

The reason settlements were batched was to save on wire fees.