The article seems to indicate the vast majority were “mint state”. At least, they were apparently in damn good shape, and it is gold, which is basically impervious to corrosion. I don’t recall anything in the article indicating any coins were pretty worn or corroded.
Yea, which is why they think they were stashed at the time they were minted generally. If they’d been taken from general circulation they’d be worn. These were like they got picked up at the bank their first time out. That’s why I speculate they were, at least in the early cases, possibly “free coined”, i.e. someone obtained gold either in trade or prospecting/mining and subsequently took it to the mint for trade to gold coin.