NOS Panels like '69 Z-28

[indyjps]

one of the reasons for thinner gauge sheetmetal is improved steel technology and higher strength steels. stamping has come a long way since 1969. even if you found a NOS panel witha date stamp it will list a julian date but wont list the year that it was made, so is it NOS from 1972 when Gm was most likely doing the stamping or NOS from 1980's when the dies were most likely sold off to an outside company who used whatever steel they could? what was the condition of the dies once sold off to another company? how much did GM actually care about maintaining dies once they went into service replacement jobs? all things to consider.
I personally stamp replacement (service) parts for the GM 400 (truck before approx 1992) the dies get rolled in once a month to run 600 or so parts, they get shipped with minor surface defects and sometimes do not pass the fixture checks. the thought is after a body shop welds on them and hammers them into place they will be ok.