Certain exotics were carried to year 2 so they could be upgraded to higher light levels (aka - 4th Horseman, Thunderlord, Red Death, etc.) while other exotics were left behind in year one so they can't be upgraded (aka - Ghorn, Thorn, Dragons Breath, Lord of Wolves, etc.). If you go to the exotic armor/weapon kiosks down by the Vanguard, the first section has all the year 2 exotics (those that were carried over and the new year 2 exotics) and the second slide shows year 1 exotics (those that weren't carried over to year 2). Note: You can only see exotics in the Kiosks that you have previously had. If you never got it, you won't see it in the kiosk till you do.

Your party crasher's roll... I hate it... lol

Thorn cannot be upgraded...