Why would a monster I kill only sometimes have an eye, tongue, claw etc etc?
Shouldn't those be guaranteed drops? I mean I see it has an eye when I fight it, when it is dead I see it still has its eye...why would I not be able to take it?

An efficiecy bonus for killing a certain monster type makes sense. I mean you would get better at killing them. I also think there should be an penalty for when you fight a certain monster type the first few times. I mean in that scenario it is a complete unknown so it should be harder to kill. This gives monster hunter types something to do. Maybe a bonus that goes up to 25% or something after you kill A LOT of that type?
In anycase, to answer the OP. Since we have no housing I don't reallly want to collect anything because I cannot display it. Books are what I will collect though because they go into a codex of sorts that I can pull up at anytime.