Jim- good info on the Heritage Center. Have to try that out with some of our cars and see how they look. Would be great info to have.
I'm not sure on all car lines and build sheets, but I would assume some form of broadcast sheet is still in use today. Probably just a big bar code nowadays.
This F-body website says Camaro build sheets were used until 1983, and
this site references finding 78-80 sheets behind the rear seat.
A few photos of '79 build sheets from Norwood seem to exist, but not Van Nuys. Here's one for an export car, which is pretty neat.
I can't speak with too much experience though, I've only found 1 build sheet in my life in a GM car and that was an '86 Cutlass. It was so brown and ratty you could only make out a few boxes and the perforated edges. I'll see if my coworker with a 78 Trans Am has one. He's the original owner and may have come across one at some point.
Off-Topic: I found the remains of one for my Mustang behind the bumper cover. It was taped up there and rotted away :(