There are two ways to view different versions of a student's work in Noteflight.
When viewing a student's work in Speed Grader you can select from each of the submissions for that assignment.
You can there select the version you want to see:
When viewing a student work in Noteflight from an assignment you can click on Versions and you'll see all of the saved versions by that student:
This could be helpful if a student is having trouble with a particular assignment and you want them to start over.