It does its job just fine.
Simply regarding the above reviews, if the salts have been absorbed for so many years, obviously they won't go away.

It requires additional preparation to be done. We can't suddenly remember to remove 20-year-old spots and expect the product to work for us.

It didn't do anything unfortunately. In black color, I have marks from salts, I did everything as the instructions say and nothing changed. They remained as they were before.