Not everyone is lucky enough to have their original windows sticker or other documents for their own cars. Sure, there are unscrupulous people in this business who unfortunately build clone cars, re-stamp engines, get falsified trim tags, have fake documents produced and then try to pawn off their cars as originals at 3 times the value of what they should be. Anyone that partakes in these ventures hopefully ends up where we would all want them to be and there have already been cases of arrests due to fraud based on the above issues. In my hobby/small business, prior to me taking on any high valued or rare cars, I share the information with what we would consider the experts in each model's field to ensure the cars are either documented or validated cars. Not just Full size cars, but Corvettes, Chevelles, Novas, Camaros, etc. Other companies may advertise that they do the same but if you look around the web, you will find many more super rare cars than were ever produced, so please be sure before you purchase any very rare cars, you have a professional review all the documentation, Vin tags, Trim tags engine stamps, etc. to ensure you are purchasing an authentic vehicle. I would be happy to help validate any window sticker for any Chevrolet Models between 1960-1970 to help out. Additionally, blank window stickers are readily available and I regularly assist others with prices if they cannot find them posted anywhere else and I'd do the same here. 35 years ago, I typed up a window sticker for my own 1966 Impala SS that I still own today. It makes a great display in a car show and most car judged car shows require a list of options in the vehicle.
Now, if you're lucky enough to own a Canadian built car after 1963 you could always go to:
http://www.vintagevehicleservices.com/options.html to get your car's information. NCRS is providing original dealer info and build dates for certain models also:
https://www.ncrs.org/services/historic-document-service.php
Hope all this information helps.
Paul