Info Panel color values are what unit of measure?

I think I now know the answer to my original questions, as I've distilled/compiled from all the info from this thread and elsewhere.

Would you please confirm if I now understand this accurately, @D Fosse , @TheDigitalDog , @Warren Heaton10841144 , @Test Screen Name , @Semaphoric and @davescm (and anyone else that reads this!)?

1.  The RGB #s are not percentages, and they have no unit of measure; they are numbers on a scale of 0-255, where 0 is the darkest of whichever color it refers to, and 255 is the brightest of whichever color it refers to.

  0-0-0 makes total black

  0-128-0 is no Red or Blue, with medium Green

  0-255-0 is max (saturation and brightness) Green

  128-255-128 is max Green, slightly muted with medium Red and Blue.

255-255-255 is max Red, Green and Blue, making total white.

2.

   In this sample taken from a Curves Adjustment Layer, the CMYK number values that do not have a percentage symbol next to them (preceding forward slashes and number values that do have percentage symbols next to them) actually are % values. (64, 51, 50, 75 in this picture)

For example, the "C: 64/ 72%" in the screen capture above, should read "C: 64%/ 72%" (including the "%" after the "64")

***Why not put that ONE extra character in there for clarity, Adobe??***

3.  CMYK values (which are all/always percentages, even if no percentage mark next to them) are on a scale from 0%-100%, with 0% being none of that ink being placed, and 100% meaning that whichever printer or press is used will as much as it can at any particular area with whichever ink(s) the 100% refers to.

There is no way to know/see exactly what that "100%" ink amount will look like printed until there is a print of it to look at.

There are color management profiles that can be selected in PS (and more that can be added to PS) that will help by displaying an on-screen approximation of what a 100% ink setting (and all other settings on PS) will look like printed, but it may take trial and error, printing until one becomes familiar with how the image on the screen relates to its print on any given printer.

4.  The numbers/values to the left of forward slashes refer to values before an edit, and the numbers/values to the right of forward slashes refer to values after an edit.

For the CMYK values, it's percentage of ink. Like, 100% C is the maximum amount of cyan ink. 50% C is half as much ink as that. And 0% C is no cyan ink at all. If all the CMYK values are 0%, there's no ink at all, just blank paper. 

And also note that the actual numbers refer to your working spaces. The numbers will vary in different color spaces.

That's why, for instance, 128-128-128 does not necessarily correspond to 50% K! It will only do that if the RGB space has the same tone curve (gamma) as the working gray, which it won't have at default settings.

The percentages are for CMYK and Grayscale, and refer to the ink coverage  — 0% is paper white, 100% is total ink. Halftones are in between.

The non-percentages are on a scale from 0 - 255, the range of 8 bits (even for 16-bit images).