Sorry, my bad. So the fenders were stamped out with no holes and then were drilled along the way during the assembly process correct?
Yes, that's correct - it's noted in the "Chevrolet Sheet Metal Subassembly" section:
<<Chevrolet Assembly - Front Sheet Metal Subassembly
All the color-painted exterior front sheet metal panels, plus the black-primed radiator support, inner fenders, and center grille support and the low-bake painted grille were conveyed to the sheet metal assembly area; all were in "Broadcast" sequence, matching the sequence of bodies on the main assembly line. Option holes for engine emblems, antennas, Vigilite housings, nameplates and moldings were pierced in large hydraulic fender piercing fixtures before the fenders were placed in the assembly fixtures.>>