I've found the various ColorChecker cards to be reasonably stable over time. The biggest problem I have using them is that the spectral response differs on some colors from that of CYMK printers. In particular A2, A3, and F2 (Orange, Blue, and Orange-Yellow). These are the colors I see the most metameric failure on with cameras and scanners. Haven't really had much of an issue with change over time with any GMB or XRite Colorcheckers. They have been quite stable.