How would you treat the Verdigri?

Thad, do a little test for yourself. And yeah I've done it.

Take a coin that has fairly newly formed verdigris on it, in other words verdigris that is still powdery. Scoop up or scrape off a little of that verdigris and place it on a copper coin. Then put that coin in an airtight container and just leave it there. A month, 2 months, or longer, doesn't matter. At the end of the time period, whatever it is, take the coin out. What I've seen is that you can simply blow the verdigris off and there will be no corrosion on the subject coin. I believe you'll see the same thing.

In the scenario you describe and in the pics - I don't doubt that for one second, not at all. But that's a long way from being the scenario I'm describing.

I also do not disagree with this -

Yes, the powdery verdigris can and will absorb additional moisture from the air. And that will help the corrosion process along because of the additional moisture. But in that case the coin is being left out in the air and moisture - where the corrosion would occur whether the verdigris was there or not.

We've both also seen many, many examples of coins with some verdigris on them that were sent in for grading. And once the coin was returned, and then stored properly, no additional corrosion occurred and no additional verdigris was formed on the coin. Not even after a period of years. This also corroborates what I'm saying.