1879 S Morgan - What is this on the reverse? [gelöst]

Greetings
I appreciate this community and recently bought this coin graded MS63 by NGC. What is the discoloration near the "AM" in America? It is also below between the wing and wreath as well.

Hard to say exactly but I believe some type of foreign substance that prevented /protected those areas from naturally toning evenly with the rest of the coin is my best guess. It does not appear to be corrosive however.

That brings a little bit of relief. I was worried someone had damaged the coin before it was put in and it would get worse over time or it was a fake. Thanks again!