This squares nicely with my understanding of what "reserves" are when talking about extractive resources. Namely, the known quantity of a resource that can be

This squares nicely with my understanding of what "reserves" are when talking about extractive resources. Namely, the known quantity of a resource that can be extracted in an economical viable manner using current technologies. So there are a number of variables that can affect the size of a reserve that have nothing to do with how much of the resource is known to exist.