Giving users access to mixed levels.

Hi I am trying to set up an e-learning membership site.

There are 25 different courses. I want to be able to set up different subscriptions with a mixture of these available courses in them.
That is
Subscription A might have courses 1, 4,7,9 & 11
Subscription B might have courses 4, 5,7,10 & 20
Subscription C might have courses 9,11,15 & 21
I have set each course up as a level.
If I add more than one level to a subcription then the next level is not available until the previous level expires. I want the user to have access to all the levels to which they are subscribed immediately. Is there a way of doing this ??

I am struggling with this
Any suggestions gratefully received.

Thanks