One often sees that said, but CMYK was (and still is at times) colour separations for the use in non-POD, non-bubblejet/laser printers. POD machines do not use printing plates. Granted, for colour they do use CMYK (and black) cartridges, but in a single pass, not as individual plates in four or more printing processes.
What I use to create my images is simply set to 'millions of colours' and I work on and Save as (for my covers) jpgs. The art/photo prog I use is capable of setting an existing image to CMYK, and if I ever try that option it literally separates the colours (just those four, and black) in to individual images. An interesting effect, but unnecessary!
Myself and my friend combined know everything there is to know, but he's not here.