"Validation of the historical data by resampling is not possible as no access exists. Confidence in the general validity of the data can be derived from the maintenance of consistent sampling and analytical techniques for sampling and grade control throughout the active mine history. The 2017 drilling also provides some validation in confirming similar location and tenor of mineralisation. However, in the absence of validation sampling or QAQC, the historical data can only support an Inferred classification for the Mineral Resource."
I think relying on historic records where there's no way to verify the authenticity and validity of data is problematic. In this case though, there appears to be so much data maintained throughout the mine's life. Couple that with the recent drilling it seems they have little doubt about what's under the ground.
This and the announcement about the exploration potential means this is definitely a long term hold for me if they get past the next two hurdles: government approvals and funding for the option.