Under the standardised University Turnitin set-up, after a student has submitted to a Final (on time) Turnitin Assignment (submission point) they can update their submission with a new file any time up until the submission deadline.  This is useful in the case of accidental submissions of the wrong file (although they can only see their Similarity Report once, after the deadline). 

If you add feedback to students’ work before the submission deadline for Final (on time) submission points, you will see this notice:

Turnntin warning prompt stating: "This is a draft submission. Any and all marks will be deleted when or if the paper is resubmitted. Would you like to continue?". Buttons available are "OK" and "Cancel"

This does not mean the student has submitted a draft to self-check their work – there are separate submission points for this.  It is a warning that, because you are adding feedback before the submission deadline, your feedback will be lost if the student updates their submission. 

Note: this is not the case for Final (after deadline) submission points.  Students can make only a single submission to these.