I would chime in here on the note regarding exceptions (i.e. user and group overrides) - such overrides REALY have to display correctly for individuals (and group members) that have been given them.
ALSO, let's not forget that in Assignments it's also possible to grant an extension of the due date - those extensions should also show correctly for students in the Calendar, in their upcoming events block in courses (if used in a course), as well as in the Timeline lists of course - if the assignment is not yet done, if another attempt has been opened / granted for the student (and work is not yet submitted), and (possibly also) if a completed submissions has been reverted back to the draft status by the teacher.
ALSO, let's not forget that in Assignments it's also possible to grant an extension of the due date - those extensions should also show correctly for students in the Calendar, in their upcoming events block in courses (if used in a course), as well as in the Timeline lists of course - if the assignment is not yet done, if another attempt has been opened / granted for the student (and work is not yet submitted), and (possibly also) if a completed submissions has been reverted back to the draft status by the teacher.