This is useful however, one thing to note: in the case of a student who has performed a quiz when grade book fields were already inadvertently over-ridden - the quiz results will not copy over to the gradebook if you manually update the database.
There is a trigger that will re-write a quiz grade to the gradebook via the interface when you click on the over-ride checkbox.
In my case I may run a query to over-ride all but one record in one course and then manually do the last one just to get the trigger.
Or you could probably also just do a re-grade of the quiz and theoretically that should re-write the scores to the gradebook as well.