<< Now I suppose GM had tin from the sixties around. I dont think so. If modern tin is so much better why did GM stamp new fenders out of full guage metal. Remember all asian tin is made from the ground up cars and appliances we send overseas. >>
It's not a matter of "having tin from the sixties around" - the print calls for a given sheet thickness, and that's what the draw, trim, flange, and pierce dies are designed to work with. Steel sheet is available in any thickness you specify, and there's nothing "special" about the sheet gauge used in the 60's; many different gauges of steel sheet are used in different parts of the car. Domestic steel isn't "virgin" either - normally it's about 40%-50% recycled material, and has been for decades; the alloying materials are what gives it specific properties.