Hello,

If you use Activity completion settings "Student must view this activity to complete it" and afterwards change the course completion or activity completion settings all past student completions are lost forever.

If you use something like "Student must receive a grade to complete this activity" Moodle can find these out even if you change course completion or activity completion setting or take course completion to use on a course that haven't had it before.

I see it would benefit old courses that take course completion to use if "Student must view this activity to complete it" markings could be retrieved from database so they should be written there just like grade information