Patone decided to use LAB formulas in CS6. So, if you call up a specific Pantone number and then convert to CMYK in Illustrator you get different CMYK percentages than what is or has been communicated in their swatch books. I recommend bypassing converting, instead just build your own CMYK swatch based on the swatchbook. This would be just to comply with your pre-existing workflow. But, it means creating 2 files, one Spot, one CMYK for whatever is appropriate for your situation. Obviously the Spot file goes to the print vendor, the CMYK file you build stays with you for proofing. Sidenote: I have seen some screen shots of users who had previous CMYK files next to a newer LAB>CMYK version and, on screen, the color "looks" closer to their ( Pantone's ) swatch book samples. But users are reporting the files print much darker than before and no longer match Pantone's swatch books. Go figure.
If users have darker print from Pantone (lab) to CMYK, it is simply because they are not using the proper CMYK working space profile that match their printing condition.
If you want to use the Pantone+ ColorBridge CMYK values, make sure you that thoses CMYK build match your printing condition. I have made several tests, I haven’t found yet how those CMYK builds could make a decent Pantone simulation. Just try the Pantone 424 or 425 (a simple gray).