We had a customer come for a press check with a sample of a job we printed a few years before. It had yellowed a little. But reprinted brochure was going in the rack with what was left of the originals and they wanted the new printing to match the existing brochures (not the standard the originally set). In particular, they wanted to match the slightly yellower cool grey 3 we printed. The old sample was about 2 greater in b* than the swatch book. We explained that there isn't any yellow in cool grey 3 so remixing the ink wouldn't make it any more yellow.
That didn't matter, so we had to make a new cool grey 3 with a little pantone yellow in it. Twenty years and ten reprints from now, that bank's corporate color will be Pantone 103 and they won't have any idea why.