Games : Duplicate items with different statistics in Destiny

I have recently bought Destiny, and I have noticed that I seem to acquire many duplicate items. For example, I have three Firebreak helmets (however one of them is Firebreak Type 4), and I also acquired three Trax Callum I scout rifles, (although I have dismantled two of them). However, each of these items says that they unlock at different levels and have different attack powers/defense points, even though they are the same thing.