hi there!
the information doesn't repeat. or, rather, the lessons don't repeat. but certain grammar points will be touched on again and again.
depending on your level it may behoove you to start from the beginning.
but for example, we started a new Newbie series and we're at about lesson 7 or 8 now. so it would be easy to catch up with if you're just starting out.
also, we have a smattering of each lesson type here:
http://www.japanesepod101.com/help-center/the-courses/
Also, our search engine is pretty cool! so if you're looking for something specific that we have already covered, that's a good way to find it.
also, feel free to chime in on the message boards. a lot of people just listen to every level, simply because it's not bad to review (or because Beginner Season 2 is kind of a wild card series, covering lots of interesting stuff!)
marky