Our shop is G7 certified. We had one customer have a difficult pantone yellow that no-one could replicate, even the ink manufacturers can't make this pantone (actual pantone) the same every time. Every color book we had was different out of a batch of I think 5 brand new books at the time, none of them were the same. We had the customer come in, pick which one they liked, and made up CMYK builds and print out a sheet of different swatches we made up and got one that matched for coated and uncoated stocks. a bit of a headache, but at least their stuff looks the same across the board.