I believe that I was the person who first introduced you to these rules, but now, I have to caution you that one has to take such "rules" with some leeway, not as precise guides and be careful when giving cmyk-by-the-numbers advice.
1. Specifically, if the light varies from point to point across the face, one has to be sure to average a sufficient number of points to get a good estimate.
2. In addition, one has to disregard simple, unimportant changes in overall exposure - this is why rules based on ratios, not absolute numbers are better.
3. Also, "Asia" is a big place with large variations in skin color based on ethnicity, geography, gender, age, exposure to the sun, etc.
4. Finally, one has to consider the subject in the context of the ambient lighting. For example, if your subject's CMYK values look perfect by-the-book, but you are evaluating a photograph of them on the beach in the late afternoon, with so-called "perfect numbers", they will look like they were lit by a strobe that wasn't gelled to the ambient light, ie, much too cold.
In the case of this image, I selected a large fraction of her skin area (carefully avoiding hair, eyes, nose holes, lips, etc.), cut and pasted that to a separate layer, and then used the "average" command to get a good overall figure. However, if, say, her neck was in deep shadow, or there were blown highlights on her forehead (say from oily reflections), I would have excluded these areas from my average.
The table you cited gives the following ranges:
c = 17 to 8
m = 50 to 30
y = 58 to 48
k = 0
By my measurements, the average cmyk value for her skin in his "after" version is 22, 40, 50, 1. Thus, magenta and yellow are right in the middle of the desired range and black is within one percentage point. The only one that is a bit off is C, and IMHO, that's just not far enough off to worry about.
For comparison,
this web site gives a slightly different (1 ratio used), but typical rule for asian skin as:
Asian/Hispanic Skin (typical CMYK ratios)
1) Cyan = 1/4 –1/2 Yellow
2) Magenta + (0-15) = Yellow
3) Black values may exceed 0 if skin is dark
4) May have higher CMYK values overall (vs. Adult Caucasian)
So, checking against this scheme:
Her cyan is 55% of her yellow instead of 50% - very slightly high again;
Her yellow minus magenta is 10 - right in the middle;
Her black value is 1 - no problem there, either.
In the final analysis, you have to use your eyes, and this means you absolutely must have a well-calibrated, trustworthy monitor. I think you mentioned that you bought a new monitor. How does she look on that? As you may also remember, I offered to send you a collection of head shots with good color. I'm still willing to do so. This will allow you to do side-by-side visual comparisons with the image you are working on or evaluating. I find this an exceptionally useful technique.
Best regards,
Tom