I realize that your post is old, but in case someone comes along with a similar problem. I solved it by having a course for 2013, one for 2014, etc. In 2013, when the student enrolls, he is given access for 1 year (52 weeks) from when they sign up, even if that extends into 2014. In 2014, when they need to be requalified, they have to sign up (and pay for) the 2014 version of the course. In my case, they have to be qualified within 1 month of their base month, so I have to open up the 2015 course on December 1, 2014. Enrollment for the 2013 course is cut off on January 31, 2014.
In my case, I just feed them videos, then they answer some quiz questions. All versions of the course point to the exact some videos, although the quizzes have to be unique in each year. That way, if I update a video, it's automatically reflected in all the active courses.
Hope this helps someone.