I have noticed of late that I get drops based on what weapon I am using, for example I use heavy ammo glitch on Crota and low and behold I get No Land Beyond. I tend to be a pistol wielder and received all exotic hand cannons fairly fast. The weapons I am missing are red death (never use pulse rifles,) Midas multi tool (usually save my scouts for PvP) and ghorn (never used rockets before CE.) this is probably not the same for every one but that is how it works for me, I finally received suros and after playing with it for a while I received two more, same happened with the vex, hard-light and Monte Carlo. My new superstition is that if I use a legendary in the class of the weapon I want to drop I will have higher chances.