I'm wrong, too!
My first set of reloading dies were Lee-- .38/.357, Carbide, purchased in early 1988. They look exactly like all of the rest of my dies, so I may have just missed the plastic seater by a few years.
Good to have the mystery solved -- I'm still curious about that REALLY short flare die with the philips metal screw in the top of it. Was that an early version of a Lee flare die?