It was SOP with the big 3 back then. Some years ago a few GM prototypes from the 50’s that were supposed to be crushed were found in a junk yard near Flint.
Still being done today 64ssa, however they are trying to go to “virtual prototypes” as the cost per unit is quite hefty, and they have cut down the numbers of prototypes and mules dramatically, with CAD/CAM/FEA/FEMA etc and “other” cost reducing strategies...