API late_policy_status for excused

[wjlane]

I need to display a submissions status on our website but I feel I'm missing something regarding "Excused" submissions. Under marks the status of a submission can be none, late, missing or excused.  But the api says the late_policy_status :

Can be late,  // missing, none, or null.

If the status is set to excused it returns null and if it's not set it returns null.  Therefore you can have an ungraded submission that's excused or unset (and so not excused) both return null.  therefore I can't be sure when I should show the submission as being excused.  

Has anyone struck this before? Am I missing something?