THC, CBD, CBN all are cannibioids, they all have variable effects on each individual and modify each other as well. I think that when tests are done on any one strain/variety the percentage they are referring to when they state that "this is 25% THC", is that of all the cannibinoids present, that 25% of the cannibinoids are THC. The final makeup of just how much of each goes into your plant is genetics, we can harvest to optimize one or the other though. I have been trying to adjust my vaporizer as I was told that you could perhaps vape at lower temps for the THC and raise it up later for the CBNs, not sure how this would work as both molecules are so nearly identical.