Study.com - once a course is completed..

[bushysmalls]

Basically, there are two areas, one showing enrolled classes and the other showing completed classes.  If you go through your dashboard, make sure it indicates the completed status and showing your current grade or percentage.  If it shows with that detail of information, it will also note a completion date as well.

So I do now see it under the Completed Courses section of the My Courses tab (I was only ever really checking in the main Dashboard section), with Date and Score, but it didn't fall off like the earlier poster mentioned.