Disappearing grades

QUESTION
I have noticed something bizarre going on with my grades in the last
couple of weeks. I have classes that have taken several quizzes (6 or
8) and when I click on "see grades", I notice that an earlier quiz
(like the first one) has several grades that have disappeared. The
kids have taken the quiz, I have recorded those grades in my grade
program, but now when I look at them, the majority of them are blank.
This has happened with more than one of my classes in the last couple
of weeks.

ANSWER
 The grades table shows grades for a certain time period.
 When you open the page it shows you grades from the last month.
 There's a selection control at the top left of the page which lets
you choose the time period to see.
 Select "All Time" to see all grades.

FOLLOW UP
Yes, that works!  Thank you.