I simply wouldn’t believe it.
There’s no way so many people could keep something that big quiet for so long.
It would be more than just the leaders, there would be thousands of people involved over the course of decades. Someone would have spilled the beans at some point by now.
I live in an older town about 700 miles from the ocean, they recently restored our courthouse with a new copper roof to replace the one from 1824 and it had a green patina in less than a year.
I don’t think salty air is a requirement for patina, just oxygenation.