All,
One indication to determine if the hood is original to the car: check to see if it is date coded on the vertical side flange in the driver's side back corner that faces out to the side of the car. To my knowledge and research, most all the factory installed hood regardless of the hood style (flat, ZL2 cowl induction hood, or SS hood) are date coded. It can be difficult to see and primer and paint might have filled in the digits.
The body trim plate on my '69 Norwood build RS Z28 is "05A" for the 1st week of May. My Camaro includes an original ZL2 hood dated "18" for the 18th week in 1969 which mean the hood was fabricated between 4/28 - 5/4/1969. Unfortunately I do not have the original paperwork, POP, etc. so I cannot be 100% sure this ZL2 hood is original to my car, but the corresponding dates code are a good indication it is the original hood. My car is loaded with options so whoever originally purchased my Camaro check nearly all the option boxes!
YES....I do have the NCRS shipping data report and the original selling dealer, Glockner Chevrolet in Portsmouth, OH which is still in business and an interesting story! Unfortunately they had a warehouse fire and lost much of their old sales and service history. That was a big bummer.