Quarterly, as a standing review with an owner — checking that stage mappings, goal records, attribution coverage and expansion ownership still match how the business runs. Reporting doesn't break in one event; it drifts through four or five small, individually reasonable changes.
The audit checklist is short: has anyone added or renamed a stage, have goals been reset, has expansion changed hands between teams, has attribution coverage decayed. Each of those silently changes a headline number, and each is invisible unless someone looks on a schedule.
Every claim above comes from work LeanScale published. These are the sources.