what probably made them dig deeper is when they saw both holes...

what probably made them dig deeper is when they saw both holes show nothing. they could not know there was a typo that placed those two holes about 100m to the west.
if they are to review/trace every historical hole for accuracy then the cost of doing that will be equal to the cost of those two holes or thereabouts. also, those are not deep porphyry holes and while still expensive they are not as expensive you one may think.

also to point out many other companies have experienced same challenge in the past and many can't even workout where the mistake was.
in SVY case I they worked it out as they found documentation on who's property the holes were drilled (Brady's) and this family property boundary is the fence along the road - the east of the road is their land while another family owns the west side.
In short if the holes were drilled on Brady's property then they were on the east side of the road. I think SVY found further evidence to work out the exact spots too.

plus every hole tells a story - in this case they know for sure there is no shallow mineralisation west of the road so their focus will be east-northeast.

to sum it - I can't blame them on this one. they did follow same path many others do. And I am not shy from being critical when warranted.