Both proctoring and gradebook manipulate persistent subsection overrides. Proctoring also enables course team members to clear the corresponding overrides by deleting an attempt by using the little "x" buttons beside the attempt in the special exams section of the instructor dashboard.
Clearing a learner's attempt does not delete PersistentSubsectionGradeOverrides written by gradebook
We anticipate the existence of a "system" field describing the source of a persistent subsection grade override which we can use to distinguish between proctoring-sourced overrides and gradebook-sourced overrides.
To achieve this we may have some older gradebook-entered overrides for which we haven't backfilled the system from which the override came. Backfilling/making sure we have good behavior for those is out-of-scope for this ticket.