I have a question to owners of Pantone Guides. How your guides change after years? I mean the colors, not technical condition. Pantone recommends replacing the guides after one year of use, but is it necessary? Do you have the opportunity to compare old with new guides?
Also depends on where they are stored. if in a dark drawer and only pulled out when used, they will maintain accurate color longer.
I've never replaced mine just because it's been a year -- I mean Pantone just wants money. Wish I could tell clients "It's been a year. We need to redo that design."
I replace mine when I start feeling like the colors aren't matching press-proofs/chromakeys.
My experience is that yes, the colors do change but in the end it really depends what kind of use you are making of your charts. The Pantone people are obviously responsible for consistency so they won't outright tell you that your charts might be fine for a long time.
If you are trying to match things like fabric that goes on a book cover to a Pantone that will be right next to it, I would go for the most recent chart I can find. For things like fine arts, books, branding, stuff that has a long shelf life.
Most of the time, I use my charts (probably 10+ years old now) to double-check how certain colors transition from PMS to CMYK. Sometimes I curse because I don't have all the fun new colors in them. Usually I just have access to newer charts in my workplace. If I'm really in doubt, I'll check those.
I am guessing your question might also be due to the costs that changing charts every year imply. Depending on where you are located, they might be tax deductible if you're a freelancer.
EDIT: Somewhat off-topic but I like my old chart because the numbers are easier to navigate, whereas there were changes made in other years that changed this around and I prefer the old way -- old habits die hard :-)
Pantone LLC updates its products regularly for 2 Main Reasons:
New Colors are added in the products.
Weather Conditions and Aging: It Reduces the quality of the print and color on the guides/books. Thus accuracy, which is the most important reason of purchasing a Pantone Book, as a result reduces. Recently Pantone has added 112 New Colors in Graphics Books and 210 New Colors in Fashion, Home & Interiors.