If a student submits the same paper to multiple assignments in the same class, those submissions will not match each other thanks to the default self-match exclusion. This is to allow users to make draft submissions without papers matching themselves. The self-match will show up in the "exclude sources" section of the Similarity Report and can easily be re-added to the report.
However, a self-match can occur when a student submits the same paper to assignments in different classes, where at least one of the assignments is set to save papers to the repository. This is because papers submitted to different classes are not automatically excluded as self-matches. If required, instructors can exclude any self-match.
Guidance on excluding matches and restoring matching is available in our Help Guide on Managing exclusions and filters in the Similarity Report.
Note: Removing a paper from the assignment inbox does not delete it permanently. Therefore, a paper removed from an assignment may still be found as a matching source if it was submitted to the Turnitin repository.