Didn't know that, is the VIN stamped (on the lid) on '73 cars as well?
Far as I know they never put it on the lid. The lid is too easily replaced I suspect. The hidden VIN should be on the driver's side channel under the weather strip. It should be under the strip directly across from the die number. These locations did vary by model and year. As I recall some also had the hidden VIN stamped under the trim on the A Pillar. An example of trunk style making is attached.
Dave