The saddest truth about old puppets is that aging latex does not last very long. Cloth puppets last for a good while, but latex loses its stretch and it simply crumbles away. Often it has also been extensively sweated into, back when it was used. Hensons are pretty good about both preserving puppets, and also good about disposing of them (I don't want to know how they do it. the idea of a skip fulled with puppets is a sad one; the idea of an underground tomb filled with quiet, rotting puppets is a deeply creepy one...). Most of the ones Dave and I played with were from a box that had been rescued from the tip, but weren't really ever going to be useful -- or used again -- as puppets.
neil gaiman