Actually, they say that the circa 1970's 1980's stuff is really good. It is when they mass marketed that they said there quality went down. Even before the shows started airing, there are threads saying that their calls were guaranteed to stick.
Thats why I like Doc Calls so much, the only time mine have ever stuck was when they were frozen solid, but a couple second blow through the back of the call and you're back running again.
He modifies the tone board in a way I haven't seen anyone else do.
http://www.doccalls.com/stick_proof.htm