Well didn't they send ANOTHER 500 samples off for testing from...

Well didn't they send ANOTHER 500 samples off for testing from the stockpiles? This indicates they are not sure whether they are hitting their targets of ~2.1 ounce per T due to something in their processing line or due to there being less in the stockpile than thought. I would say it is a bit of both as clearly they had issues ramping up and made specific mention of there being 25 times more "dore" than with gold as if to say that was an issue.

When loosely packed dirt is piled up you will find over time that the heavier particles will sink to some extent as the dirt settles, channels will form with the help of rain and drag inward some of the heavier silver/gold and associated ore. Though I wouldn't think it would be much more than 10% on average, but either way they will find juicier stuff towards the bottom of the piles. Those stockpiles have been sitting there for a while but you are never going to know for sure until you run it, but by sampling it you will be able to make better guesses which it seems they have now. They might discard certain sections so as not to run unprofitable stuff through, and may also find sections with >10ounces per tonne. That is the fun with mining, they could have had a hot streak sitting in that pile for a long time and never have known and you will usually never know until you actually run it. Sampling just makes the guesses better.