The relevant management system documentation of the auditee should be reviewed in order to establish an overview of the extent of the system documentation to detect possible gaps.

Specifically this is the SHALL requirements of ISO 20121 where it refers to documentation.

See a list of documentation requirements here.

The documentation should include, as applicable, management system documents and records, as well as previous audit reports. The document review should take into account the size, nature and complexity of the auditee’s management system and organization, and the audit objectives and scope.