This may either be exact checks (for example, against the same data source) or sense checks (against similar data sources, but perhaps with different coverage/definitions/time periods).
yn erbyn yr un ffynhonnell ddata) neu wiriadau ystyr (yn erbyn ffynonellau data tebyg, ond o bosibl gyda chwmpas/diffiniadau/cyfnodau amser gwahanol).