I agree the "twinning" plan seems pretty unnecessary, particularly given the number of historic drill cores that they DO still have available to use. The result provided seems an artifact of one particular assumption made, and the particular bit of math done in the statistical modeling based on that assumption.
With an adequate reason (that might not take drilling 10 holes to find) you might easily use a different assumption, or a different statistical model... or both... and come up with a vastly wider range of potentials in how to address answering one question re statistical validity... all still well within "the rules"...
More than one way to skin a cat...
Drilling 10 holes is one.
Maybe there are a couple of others.