What skins can knives come in

With regards to knives in CS:GO, you inflict the same damage to an opponent with a knife to the head as with a knife to a leg. The extra damage element is caused by knifing from the front/side or the back.

This weapon chart shows the knife damage of the primary and secondary attack, to each hit box area (although irrelevant) and also whether in front/side or behind your opponent. As you can see, the hit box area causes no difference in damage.

Interestingly, this chart shows that kevlar and helmet mitigate knife damage. It also indicates that it reduces the damage when hit in the legs. Kevlar doesn't reduce damage to the legs with any other weapon. This seems to indicate that knife damage is based solely on whether hit from the front/side or back.

If we relate to the model that is shown to us when we unbox items, i think that the possible listings are shuffled and then laid in a random order but with the very valuable items in the extremities of the list. I think when a case is opened, a random number is generated somehow that it has some kind of an average number, and average weapons standing in the middle of the list. From what i've seen on many unbox videos on youtube, if the roll is higher (you get further in the list), there is a greater chance to get a better weapon. However there are still some common ones past the "middle" area of the list.

I think nothing can be said certainly, just as in Dota 2, there is no certainty that you will get at least a mythical (or unusual) from a chest with lots of rares.