A points scheme becomes a liability the moment it stops being predictable, and the two commonest ways that happens are tiering on the wrong number and retro-fitting expiry.
Tiers key on lifetime spend, never on lifetime points. A tier carries an earning multiplier, so tiering on points creates a feedback loop where points buy a multiplier that buys more points — and any historical over-accrual becomes permanent.
Expiry is forward-only. Which earning a past redemption consumed is not recoverable from the ledger, so no expiry date is invented for a historical balance; those points simply never expire. New points carry a lot with a date, consumed oldest-first.
A hand-set tier is locked and survives every nightly recompute, because silently demoting a guest the property told they were Gold is exactly what the flag exists to prevent.
The whole module ships inert — expiry disabled, no tiers seeded — so enabling it is a decision rather than a surprise.