Oops! Forgot to mention that the Illuminant/Observer is 65/10.
As it happens, I have four swatch books with 267C. I used an EyeOne Pro spectrophotometer to read the swatches. I usually have it set to D50/2 observer and actually have never used D65/10 before, so I hope I did it right. I used QuickRead to take spot measurements, with all samples sitting on a white background. Here are my readings in Lab units, with D65/10 observer:
1. 28.91, 33.12, -50.30 Pantone Solid to process guide
2. 28.82, 33.96, -51.33 Pantone Formula Guide
3. 27.09, 32.23, -49.47 Pantone Solid to process guide
4. 28.31, 33.61, -50.97 Pantone color formula guide
These books are 4 or 5 years old, but they haven't been used a lot and they are kept inside a black case, away from dust and light. The above is a reasonably tight grouping, but number 3 is odd man out.
I just reread swatch No.1 above with my spectro re-calibrated to D50/2. It gave me 25.63, 41.63, -54.51, which is very different, so I believe my spectro and the software are probably giving the right values in the grouping above.
Hope that helps.
FWIW, I checked my D50/2 readings against the Pantone Solid Coated library in Photoshop (loaded with PSCS2). They are pretty close.
My D50/2 spot reading: 25.63L, 41.63a, -54.51b
Library in Photoshop: 25L, 41a, -55b (of course, Photoshop rounds off L*a*b* to the nearest integer).
Thanks for the info, Lou! Looks like I've got some more research to do...
From the two swatchbooks I have on-hand at the moment, I'm getting very different numbers (esp. the b values):
L26.85 a41.94 b(54.40)
L27.97 a27.34 b(39.85)