HS, thanks for the reply. My comments in italics below:
What CMYK paper swatches?
Digital Color Index by Alan Weller book and CD
How can a new book that's 5 years old be a sentence?
When it was printed in 2011 but never sold and remains in it's original packaging
CMYK paper swatches show you the colour breakdown for CMYK on the computer and how it outputs on that specific paper.
There's many different printing situations, Digital. Litho, Screen, Large Format. Flexo, etc. so it depends on what printing process too.
RGB defines it's closest match via the screen. Your monitor, someone elses monitor, your phone, the web, etc. Each screen is different and not all screens are calibrated the same.
If you use the CMYK mix on the paper swatch, then communicate that with your printers, and provide the same colour sample so they can match.
But RGB is only required for on screen.
I understand what you say. For printing yes I see that if one tells the printer to use cmyk color x on paper similar to the swatch book the color printed will be close to the color swatch. When one is setting up a design on screen one is using rgb colors. If I am happy with the colors I see on screen I thought I could try to match them with the printed cmyk swatches and specify those to the printer. So under that scenario the rgb numbers on the swatches serve no purpose. How else would one do this? You can see I have never done this before.