POLICY: Should automatic 'completed' status remain once granted, even if settings or data change?

There is an open policy question:
Should past activity completions might be retroactively changed by changes to settings?
That is, after a student completes an activity and it's marked as "completed-passed", "completed-failed", etc., might it later become "incomplete"?
As one example, a student might complete a Quiz, with a passing grade. The quiz is marked as completed-passed, which opens up a Certificate. The student prints the certificate and files it with regulators. Six months later, the teacher decides that from now on the passing grade should be higher. The teacher changes the "grade to pass" setting. Should the student who completed and passed six months prior now be marked as "failed", and their certificate revoked?

A dev docs page on the question exists here:
http://docs.moodle.org/dev/Policy_-_Retroactive_effects_of_completion_settings

Discussion on the forum took place here:
https://moodle.org/mod/forum/discuss.php?d=226129