Capture concept of "current" grade

There have been community needs expressed for a standard way to capture the concept of a "current grade" - a grade as it currently exists in SIS (or possibly, gradebook, if those are not the same system).

The Landing Zone project created a GradeType descriptor value of "In Progress" and defined it as 

"A grade for a grading period that has not yet concluded." 

That might be a good starting point.

There is probably ALSO a need for normative best practice description relating to management of this resource via API - these seems to be applicable questions:

• Since such a grade is volatile, are there expectations with respect to when such a grade is updated? Is a "periodic" update expected, or should it be updated when there is a change? 
• When a grading period completes and a grade is finalized, should this grade be deleted? Or should clients just ignore it? Note that the natural key of this element means that the end grade for a period and the "in progress" grade are two different entities.