Valid, Expiring, Expired statuses in Courses and how it works.
The Certificate Expiring status depends on the 'Certificate Expiry Reminder' settings (set in the Notifications section).
If we have Certificate Issued 5/4/20, Certificate Expiry date 5/31/2020 and Reminders: 60, 3, 2 days.
The system will check only such particular dates for changing status (60, 3, 2 days before the Expiry date).
In our case, the system will check only 5/28/2020 and 5/29/2020 (3, 2 days before the Expiry date). It will not check 60 days before as a timer job cannot check old dates.
So the status will be changed to 'Expiring' only at 5/28/2020.
But if we have 'Certificate Expiry date' in the past there is only one way how to change the status - re-enroll users manually.
Remember, it is possible to have several 'valid' statuses.