@kwarner65 -
Is this quiz a classic quiz or a New Quiz (just in case you are new, these are the 2 types of quizzes you can create)? My guess is that you used New Quizzes. In new quizzes, it is possible to make the point total of the quiz different from the point total of the questions(if I remember correctly - I don't use New Quizzes). I decided to check it out, so it is possible that you have a point difference between the questions and what the quiz is worth - or you did when the students quiz was graded. Then you changed the quiz points back to match the questions. Problem now is that the grade the student has does not automatically change back to what the new quiz total is. I had to go and manually change a 5 out of 2 score to 2 out of 2 in the grade book. This was after I made sure the quiz points and the question points matched.
Not sure if the above is the case, but all I can provide at this time. I would check with modifying a single student only and see what happens - I would check the grade information for the student before the change and after the change to make sure that the score is correctly being represented after modification.
Ron