@JanetTesterman -
If you allow multiple submissions for the assignment, the latest submission is the one that is visible when you go into speedgrader. You can select the previous submissions via a drop down for that student.
Also, if you graded the first submission and then the student resubmits, it shows up as not being graded in the grade book. However in speed grader you have access to that information in the drop down menu as shown below

in the above picture I had 3 submissions - the first one is on the top, the second one I graded and the third one was after the grade. In the gradebook, the third submission causes the grade to go away and the submission document to show up.
This information is probably somewhere in the instructor guide pages for assignments