This is the exact reason why we sticker all of our hardware including phones and KSUs. With all of the turn over that happens, the person who bought the solution X # of years ago is long gone if/when a problem pops up. We usually don't even know that a new person is our Point of Contact, and our asset stickers have pointed the new POC to us more times than I can count.
They are also useful if a client goes out of business and abandons the equipment, and a new tenant takes their space.