Anytime I see stuff like this, I get curious. The two images to follow are seat back frames from a 1972 Challenger. The broadcast sheet inside was mouse fodder, so I do not have a scheduled production date for the car these came out of.

Image 1, note all the holes for mounting the spring 'basket' are there like 1971 model year seats had, but only the top rear spring was installed. The top rear spring was the only one mounted independently of the spring basket in other 1971 seat frames I have seen.

The date code on this frame is the 216th day of 1971.