Taking the last change from the system and tracing it back to the log is the best way for the auditor to confirm the change log is complete, because:
It verifies that the most recent change made to the system is recorded and documented in the change log, which implies that the change log is up to date and accurate12.
It tests the effectiveness of the change management process and controls that ensure that all changes made to the system are authorized, approved, tested, implemented, and monitored123.
It provides evidence of the traceability and accountability of the change management process and personnel, which can help the auditor identify any gaps, errors, or risks in the process123.