Valid closure of an audit observation requires evidence that the corrected process will function as expected in the future. This involves not just addressing the immediate condition but also ensuring that the root cause has been addressed and that the implemented corrective actions are sustainable and effective in preventing recurrence. This ensures that the underlying issue has been resolved comprehensively. Reference:
The IIA's International Standards for the Professional Practice of Internal Auditing (Standards), Standard 2500 - Monitoring Progress.
The IIA's Practice Guide on Audit Follow-up.