Nope it is not always necessary to listen to Session A then B for a problem. Sometimes one or the other session has all you need. So don't be surprised if sometimes you get the feeling you should be listening to Session B and have never done a Session A for it. Go right ahead and do the session B perhaps first and only.
Also it can be you need to do session A (or B) a number of times before you are ready to continue with the next level and do the other session. So do 2, 3 or even 5 session A's before doing a session B. Once you've heard both sessions you mind will be able to guide you to the correct listening pattern if you will allow it.
Alex
