Source material is held as immutable snapshots, and every answer records the version in force when it was given. Superseded snapshots are kept for as long as any log entry refers to them, so the version in your record always points at something.
Why an answer given last year can still be defended this year
Guidance is amended, provisions commence, editions are superseded. An answer that was correct when it was given can look wrong eighteen months later for no reason other than that the law moved, and a firm relying on it needs to be able to show which is which.
Companion records, for every answer, the version of the source material in force when the answer was produced. The corpus is held as immutable snapshots: a change produces a new snapshot with a new identifier, and nothing rewrites a published one. A single request pins one snapshot and uses it throughout, so no answer is ever drawn from two versions of the law.
Superseded snapshots are retained for as long as any log entry refers to them. Without that, the version recorded in the log would point at nothing, and the reproducibility would fail at the moment it was tested.
Each source carries its authority tier and its edition, and where guidance is approved for anti-money-laundering purposes, that status is carried with it. The weight a piece of guidance is given is not asserted for a document whose approval cannot be confirmed, because approval is not permanent.
The practical effect is that a firm asked to justify a decision from two years ago can produce the question, the route, the authorities and the edition of each - rather than reconstructing what the position probably was at the time.