If the lecturer selected Use repository when setting up the assignment, then the assignment will be part of the Turnitin database.  This is necessary if you want other assignments to be compared to this assignment.  Please note that the copyright for the assignment still rests with the author. 

If the lecturer selected No repository when setting up the assignment, then the assignment will not be part of the Turnitin database.

When draft submissions are allowed prior to the due date, the comparison of submissions within the same Turnitin Assignment link will not take place until after the assignment due date passes. This means that similarity to your classmates’ work will not show in the Originality Report prior to the due date.

Reports are regenerated by Turnitin at the due date and therefore the percentage similarity may change at this time.

For example, students may notice an increase in similarity after the due date if an assignment template has been used. In a situation where students have used template text such as table headers or report sections, these sections of text will only show as matches within the class group after the due date has passed, and will probably increase originality percentages for the whole class group.

Likewise, if two or more students have included the same piece of text, Turnitin will display the existing external database matches prior to the due date; but once the due date passes these student papers will also match against each other.