For 1970-72, GM issued a protect-o-plate (credit card-sized device in the glove box for warranty purposes) with each car. If you can get it is nice to have, but since many used cars are even missing the owners manual, many have been discarded over the years. Especially for cars built in Los Angeles, the protect-o-plate will tell you more than the cowl tag.
For all of the second generation, there is a chance your prospective car had/has a build sheet. Every car had one when they were built at the factory, but many never left with the car. Luckily, some were stuck in the car (probably to eliminate excess paperwork on the assembly line). Places to check are under the bottom front seat cushions, under the rear seat cushions, or behind the rear seat back.
Occasionally you will find some owner who had the sense to save the window sticker or other factory paperwork. This is extra neat.
Camaro enthusiasts in the USA can contact Chevrolet at 1-800-222-1020 with their car's VIN handy for free information. It is called the Restoration Pack (not the restoration catalog) and includes specifications, identification information, parts supplier information, information on auto clubs, and more. Allow about two weeks for delivery. Limit two per person. I ordered one for my 1980 Camaro and they even included what appears to be a copy of an original sales brochure for 1979 (probably the closest information they still have).
For Camaros originally sold in Canada, see GM of Canada's Vintage Vehicle Services to get a bunch of information.
If you strike out here or want more information, try a title search through the motor vehicle department in the state were the car was last registered. For a nominal fee, they can track the car back as long as it was registered in the state, and tell you the state that it transferred from. From here, you can contact that state for more information. Gets to be a lot of work if the car hopped around the country, though. From this, you can determine where the car was sold new and names of previous owners to use as sources for more information.
If you're looking for some more reading material, check out the Recommended Books section.
If you're trying to check codes on a car and they have been ground off or otherwise tampered with, be very suspicious that someone is pulling a fast one. Just because the date code is from the correct time period means that it could be from any car build at about the same time. If the engine/drivetrain/rearend are original, the numbers stamped on them should match the car's VIN.