Play reports only a period's end, and the service dates the charge a plan length before it, so month-end clipping could leave a charge funding less than its month. Walk a monthly and an annual Play plan anchored on 31 January through their renewals at the device's request moments, through the deployed Play verifier: each charge funds exactly its months, paid-through stays at most the grace behind Play's period end (three days at most in this walk), and no charge is left without a grant.
Run: 015-badge-fixes, slice 2