That only means that you can add wealth up to the new delta. Anything more is zero-sum.
As a result of the above, the value of a natural resource changes over time. For example, natural resources used in electronics and batteries are relatively more expensive now than they were 100 years ago.
So, you can be technically correct by saying that wealth is zero-sum, but that's pretty much the same thing as saying "the world's 'wealth' traded for natural resources sums up to 100% of all natural resources"