First, please don't cross post, that's part of the rules you agreed to. Second, many substances have more than one CAS number, that's just how it is. For example different numbers can refer to the same substance from different sources, or just extracted by different methods. That's just how the system and how the number assigning rules work.
I am afraid your second question is a bit like asking about differences between a bike and a TV set - they are so different it is not even clear where to start. What have you already found about them?