Finding a subscription in plain charges instead of reading one directly means SSA has to guess, carefully. These are the guesses that can go wrong, and why each one is built the way it is.
The weekly floor
SSA refuses to detect anything billed more often than about once a week. A chain whose typical gap is more than a day short of seven is treated as a run of one-off payments, never a subscription, and a cluster of same-day charges is refused at every setting.
Refunds
A refunded charge never starts a chain and never counts toward the minimum of three charges. Inside a chain that already exists, a refund does not break the pattern: one refunded renewal does not turn a monthly plan into a bimonthly one.
Plan changes
A detected chain only accepts charges within 1% of its original amount. When a customer's price genuinely changes, the new charges fall outside that band, so they start a brand new detected subscription while the old one, no longer receiving matching charges, lapses to cancelled once its usual interval and grace period pass.