Timestamp to show when grade status was last changed

[Jim20]

We use a 3rd party grading system with the Canvas API to send grades back and forth. I use the submissions API to see all student assignment stats for a particular assignment (e.g. grade, late_policy_status, etc.).

I've noticed that the "graded_at" field of the api tells me when the grade was last changed in Canvas, e.g. changing from Ungraded to Complete. But if the teacher only changes the grade status (e.g. from Late to None, or from None to Missing) without changing the grade itself, then the "graded_at" field doesn't update with a new time.

I need to know when the teacher last changed either the grade or the grade status. Where can I find a timestamp for when the grade status was last changed?

Thanks!