Moodle gradebook sensitivities - overiding values

One of my on site "principles" asked me about a month ago what I thought able putting 0's into the gradebook for quiz score after a deadline passed - rather than a '-' hyphen - which seems to be the default. I told him I "we do not know the repercussions of doing something like that, after all, the moodle gradebook is a little sensitive.  I did suggest that he and the teacher involved should try on a small scale.  Basic technology or life wisdom.  If you are not sure of the entire picture, the impact of something, implement on a small scale.

Fast forward 4 weeks.  I see an email from the same customer that says, all copy it

In AP Art History, Peggy entered zeros for quizzes that were overdue. When the student (Fel Tho) completed them, it seems that the system records the grade (Unit 2 Quiz Yourself 5 and 6), but the User Report does not.

I removed the zeros in the Grader Report for these two assignments, but I don't see the student's actual grades yet in the User Report.  Will they appear there soon?  

 Well - this is what i meant by the "impact of something".  Since the a manual quiz grade was given, for each quiz, - the Overridden property is checked.

From the Grader report - turn editing on to see this view of the gradebook.  Find the quiz and its question (pencil icon) and edit the grade for the question

The Overridden property was activated when a value was entered for the quiz.  When the student would take the quiz and get a legit score - that you could see when viewing the quiz attempts - the grader and the user reports do not show the score.  Immediately upon unchecking the Overridden property - the students quiz score show correctly in both the grader and user reports.

The end.