Coaches built in 1979 would likely be toughened glass and not laminated, ie single pane, so could well have had wires on it just like the rear screens.
The patent actually covered the placement of the wires on the compressed sheet between the two glass pieces that make up the laminated screen.
Most aircraft screens are not made from glass, it simply isn't strong enough, the same stuff is used as serious deep sea subs, and the record breaking visit to the bottom of the Marianas Trench, which exerted 1,100 atmospheres of pressure upon the material, or in real world terms 812 TONS per square inch, no that's not a misprint.
The material of choice is PMMA, or Poly(methyl methacrylate), in various thicknesses.
Another more common name is ACRYLIC, just a special version.
tabetha