Glossary
Policy Version
A policy version is a specific, addressable revision of a policy — not just 'the current rules,' but the exact rules as they existed at a particular point in time. Recording which version was in force for a given decision is what makes that decision re-verifiable months later, after the policy has since changed: a reviewer can retrieve the version that actually applied, rather than evaluating the request against whatever the policy happens to say today.
A system that applies 'whichever policy is current' at evaluation time without recording which version that was makes its own past decisions impossible to independently re-check once the policy has moved on — the record shows an outcome, but not the rule that produced it.