Let's sum it up as bad math on the part of the American potato council.
It is not something you can average. Soil sampling and the amounts taken each year are a factor of investigations, export samples, which are provided on demand by growers, the national potato wart survey in our current context, and other things. The number of soil samples fluctuates over a period of time, and you can't average it out, which is what the National Potato Council tried to do. We have sent corrections regarding that to the various media outlets.