It’s an urban legend that floss colors never go away. They do, and sometimes the numbers get assigned to different colors. If you believe the legend then you can get an unpleasant shock if stitching from a vintage chart or article.
Happily for us these changes don’t happen often.
However DMC is discontinuing several colors of embroidery floss.
Melita has helpfully put a chart of them with suggested substitutes on her blog. Please consider the suggested substitutes to be starting points only and always look at them with the other colors in your project.
I’m sending a big “Thank you!” to Melita!