I'm surprised the 1950 Buick Special Fastback had such a large curved rear window in one piece.

I seem to recall reading that back in the early Fifties, putting a big curve, in a large piece of glass was either hard to accomplish optically, or that it was very expensive. I understood it to be the reason most of the cars back then would have a 3-piece back window when it had a big curve. It was not just a style thing to have the sectioned-window.
That one-piece window really makes that Buick Special a remarkable styled car for the time.

Looking at pictures of the 1971 and 1972 Riviera's again, I didn't realize they also had a distinct center crease down the trunk and roof, like the Crossfire. There's even a line down the center of the rear window, like the Crossfire concept car. Maybe Crossfire drew some inspiration from this car also.