What does "not submitted yet" mean?
It means that BookWidgets is aware of a student because they have submitted at least one answer in the past.
In the results and grading overview, you can sometimes see the indication Not submitted yet next to a student's name.
This means that BookWidgets is aware of this student because for other widgets, they have already sent in at least one answer for this course, but that for this widget, no answers have been submitted (yet).
It does not mean that the student has already started working on the widget (but hasn't finished it).