Soilworker makes the excellent point that most Pantone colors cannot be hit by ANY combination of CMYK, and therefore any conversion is just a rough simulation. Pantone makes their money by creating colors that are visually different from colors that can by created by CMYK, so they have no real motivation to make it easier for you (or Adobe) match those colors. They want to sell INK, not just swatch books.
One reason for inconsistent CMYK values is that there are different kinds of CMYK. Every combination of press, inks & paper can produce a different color with the same CMYK values, so CMYK numbers only have meaning within the context of the printing condition they have been created for. That's why there are publicly available datasets and profiles published by groups like FOGRA, SWOP & GRACoL, which define a sort of average visual appearance for a given type of printing on a given class of paper (#1 coated, #3 coated, uncoated, etc.). So any software that is going to convert a PANTONE into CMYK has to consider what kind of CMYK printing you are going to be doing. First it has to look-up the L*a*b* value of the pantone color, then it has to translate to the color profile you have selected in your color settings using the rendering intent you have specified. If you pick a different profile in your color settings, you will get different CMYK values out (try it!).
I really don't know why Illustrator and Photoshop can't agree - They don't even agree on the LAB values of PANTONE colors, so their CMYK or RGB translations are of course going to be different. You would think that at least they would have the same LAB look-up tables, but apparently not. Maybe someone on this forum knows why they have different LAB start values.
Another factor is that even within a single CMYK "color space" (like GRACoL2006_Coated1), a given LAB color can be rendered by a variety of CMYK values, especially muddier greens and browns that use all 4 inks. If you want to see wildly divergent CMYK values, lookup 385 C in Photoshop and Illustrator! The point is that just because two programs give you different CMYK values, doesn't mean one is better than the other or that they will even appear visually different when printed.
Wow, what a minefield! Just as PANTONE wants it to be! Soilworker is correct in that you may just have to print out a bunch of swatches on a proofing system that is set-up to match your printing condition as closely as possible and pick the one that works best for you. IF you can get your hands on an official LAB look-up table from PANTONE, then you can convert to the correct profile and get good starting CMYK values, but you may want to do further tweaks from there.
By the way, PANTONE isn't an industry standard, they have just been around for a long time and are very well known. They are in it to make a buck, not make color matching easy.
-Todd Shirley
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