They knew the potential before they started drilling the AC...

They knew the potential before they started drilling the AC program. This is basic stuff - who here is actually surprised??

most of the historical RAB holes are vertical, shallow and often did not penetrate beneath transported cover

So not difficult to work out how deep it (mineralisation) could be. Historically, open pit was the only viable financial option. If you didn't quickly hit it with RAB, it wasn't worth it. I imagine early exploration to be a (coordinated) smash and grab approach given the POG..

Pretty much all the low hanging fruit is gone. Maybe there is the odd spot that hasn't been uncovered - but it's pretty rare..
IMO it's not 'underexplored' as AP explains it, it's been well explored, and the easy pickings have been taken.. It's been underexplored - at depth!!

I liken modern day exploration to fishing. In years gone by, you would just head out not very far, get a bag limit of big fish and go home. Now with all the technology & pressure on fish stock, you have to head deeper and further - and use all the technology available to find that one spot no-one else has, and you may do alright..