It's not necessary to listen to the Paraliminal more than once before going onto the next. It's a nice balance to listen and continue with the course. People get stuck on trying to perfect each step when doing CD courses however in most cases it's necessary to do the next step and allow the previous one to integrate.
It's like the teacher at the front of the class room. If they keep saying the same thing over and over, you start asking so? What's the point. Often the next step helps make sense of the previous point. And what you thought it was that you needed to do wasn't needed.
It applies to all courses. Do the course, don't stay with a lesson or section until you think you perfected it. Perfecting one section is like carving a carrot into a pencil and then later discovering you only needed to peel it for the recipe.
You do what you can, do the best you can and find out how you did once it's done. It's a learning experience.