What are the ranges for correct skin tones using RGB%?

While I whole heartedly agree that we should not be constrained to hard and fast numbers for accurate skin tones ... LR does offer an RGB color readout ... I am assuming they made those percentages available for the user to monitor the breakdown of specific color values for a reason ... so we could have an indication of how a specific color in an image will be reproduced ...

I liken this to using a speedometer ... while many experienced drivers in well tuned vehicles can travel on the highway at the prescribed legal speed limit without really monitoring the readout on the dashboard ... however, there are times when they would like to verify the speed at which they are traveling ... the RGB color percentage readout in LR is no different ... just a source of information to verify you are achieving what you desire ...

Again, going by specific numbers in this instance, I believe, could lead to problems ... there may be times when you may desire or actually need to adjust skin tones ... even though a pleasing WB has been achieved ... the relationship of R, G and B can be used to get you there.

From what I have researched and put into practice with LR the following seems to be a good starting point and the data was borrowed from "the pixelation" blog:

R: highest %
G: middle %
B: lowest %

To get a little more specific. In general,
R: Y + (15-20)
G: average of R and B
B: R – (15-20)

For example, the following values represent common Caucasian skin tones using the rules above:
* R: 80%; G: 70%; B: 60%. R is 20 points higher than B, and G is midway between R and B. That’s perfect.

*  R: 86%, G: 78%; B: 70% also reflects a nicely balanced skin tone.  Again, G is midway between R and B, and R is 16 points higher than B. This, too, illustrates a great relationship among the colors.