Have you wondered why you got more scratches on the Nokia Lumia 920 or Nokia Lumia 1520 than on the 1020? No? Well, Volker Weber did that and did some reserch.
Here you can see that the Lumia 1020, 1320 and Icon all use the Gorilla Glass 3 while all other use Gorilla Glass or Gorilla Glass 2. I cannot tell you why. Do you have an idea? Anyway, a very good overview in my opinion.