We use terms here to time gate a course for instructors. For example, a Spring 2017 course would be available in full for teachers until December of 2017, after which it goes into the Past Enrollment section of their courses and become read only, though they can still use it to copy content to other courses.
The problem here is that when we try to add teachers to those Past Enrollment courses, that is necessary when teachers are taking over for other's teaching assignment and need access to content for example. When you add a teacher to a "Past Enrollment' course, they do not get a course invite, the course do not show up on their course listings and they get basically no notification that they were added. While they can access the course if they were sent the direct url for the course, there is no way for them to get rid of the Pending status of their enrollment in the course.
That seems counter productive to me, I understand not sending out invites or notifications of adds for students because they fundamentally cannot access past courses. But that's not the case with teachers and there are utility to be added to past courses, what is the downside to allowing teachers to receive and accept invitations to past courses?