Thanks Mark!
And no apology necessary. I realize now the problem and the reason why unchecking the override box wasn't working was actually because I had accidentally set another value for a set of quizzes to zero, meaning Moodle was giving the final grade based only on one assignment! It's funny how easy it is to mistakenly input numbers if you aren't paying attention. Makes me a little nervous, but glad I found the problem. Thanks again!
Peter