Yes, Blackrock is called Leather n Rich.
Verdigris is oxidation. It happens to all brass unless it has a protective coating on it. Older (NYC)
Coach I don't believe ever had a coating. Newer (90s) stuff usually had a protective coating but that wears off, sometimes unevenly, making the hardware look like it's chipped. It takes a lot of polishing to remove the entire protective coating so you can then polish all the brass evenly. Some people have experimented with replacing the coating so it doesn't tarnish again.
Replacing hardware is an individual decision. I was cleaning up and discovered I have a replacement turnlock Coach sent me several years ago that I never used! Coach doesn't give them away anymore, but there are places you can still buy them. There are sellers on ebay that sell them, I think. This ebayer:
https://www.ebay.com/usr/silver-coach used to have them. I don't know why they don't have anything listed now; maybe they are on vacation.