A friend of mine belived exactly what you are explaining. Literally watched as everyone got ghorn from our regular raid fire team. (I was last to get it and his brother has had 4). He thought he would never get it, I personally felt the same about the vex having done tonnes of atheon hard cp's and seeing them drop for everyone but me. He got the horn from a crucible reward while taking part in his first iron banner earlier tonight. I got the vex last weekend from my third atheon run. I now belive something slightly diffrent. That exotics have tiers and the teirs are weighted. So higher teir weapons: ghorn, vex, thunderlord, IB, etc drop less frequently in the first place (weighting changes after first drop to fall in line with mid teir) Mid teir: suros, hard light, P&T, plan c, etc drop more frequently than high teir wepons (weighting changes after first drop to fall in line with lower teir) Lower teir: no land beyond (most common exotic drop weighted heavily over higher teirs) Everytime you get an exotic roll that re rolls for the teir of weapon you will recive. So say you get lucky and drop a ghorn then next roll the ghorn becomes easier to find even though it still needs a higher teir roll to find making the last weapons from each teir extremly hard to find (unless brought from xur) This isnt fact its just a guess at how the system works.