A subscription is charged by the day, so an invoice is arithmetic anybody can check: days in the month, minus mornings we missed, times the daily figure.
Missed mornings are taken off before the invoice is printed, and the invoice names the dates. Nobody has to notice and nobody has to ask, which is deliberate: a credit that depends on the customer complaining is not a credit.
Three missed mornings in one month and the whole month is credited. That has happened twice in four years, both times a truck off the island, and both times the invoices went out at zero without anybody telephoning us.