"...but did anyone ever see or do the assay on those drill cores?"
I'm sure they have. However, NAK's aquisition is still open (suject to liens and litigation). This means that nothing can be said by anyone as there remains a question of ownership.
Besides, I would guess that KAK has enough on their hands for now, and may not want to invite attention from those who are opposed to Pebble by disclosing a position in Big Chunk, a position that may suggest another project of similar size in the same area, albeit in another drainage.
VP