If an assignment has not been updated by a student, but has been given a mark by the teacher, then it is likely that:

1. it has been submitted in some other form (e.g. offline)
2. it has been deemed unnecessary by the teacher (e.g. it is a resubmission, but the student has already gained all the marks).

In the first case, we cannot determine if the submission was late or not.
In the second case, there is no submission to be late.

In either case, showing the current lateness is distracting and makes it harder to spot the items which really are late.

Solution: fix the grade report to ignore any unsubmitted assignments that have been marked by the teacher.