Why is it that when I change the color from spot to process via my swatch options dialog box, it is different than the Color Bridge value in my swatch book? Take PMS 200 C, for example. When I change it from spot to proecess via the dropdown I get the build: 16.5,100,86.51,6.86-- but my color bridge book is reporting 3, 100, 70, 12?
With your Adobe CC programs comes a set of color books files. They are lookup tables with measured absolute Lab colors for each ink.
When converting a Pantone swatch to CMYK in Illustrator, the Lab color of the ink is looked up in the color book and then converted to the set of CMYK values that comes closest to reproducing the Pantone ink.
This process uses the Working CMYK Profile of your document. Different color profiles will produce different sets of CMYK values.
The CMYK values provided in the Pantone Color Bridge are made using one specific (to me) unknown color profile. Using these values for different printing machines printing on different kinds of paper according to different standards will give different results. So I'm not really sure how helpful it is.
I would personally avoid using Pantone's "magic numbers" and rather rely on the conversion. And of course use my common sense and sometimes tweak the CMYK numbers if I believe it will give a color closer to what I want.
To illustrate my point, I have made this comparison (in InDesign):
The document has the color profile Coated FOGRA39 so all CMYK colors are shown as they would look if printed according to that standard.
In the top we have how InDesign displays Pantone 200 C using the Lab color stored in the color book. Below we have that ink converted to four different color profiles and the values you find in Pantone's Color Bridge.
All different values and all different resulting colors.
(The CMYK numbers are rounded and you can always discuss exactly how to preview this, but it surely shows how color profile matters.)