I have The Hooper book from 1991, Jerry's book, The new Judges Manual (2022), Colvin's Chevy by the numbers. Each book has its merits and its flaws. Chevrolet by the numbers while extremely accurate has a handful of loopholes and they're based on not enough info, or data points to confirm certain parts. The definitive 1969 Camaro guide, while good at the the time of publishing has some oversights and generalities that do not apply throughout the production year ( which some facts only became known after publishing). I have also gone through the new 1969 Judges legends manual and again good detail on some changes in production, but no part numbers on some changes, and some multiple version or interchanged parts and designs use through production isn't even mentioned for the Z or SS cars. When 100's of thousands of cars are produced and they have quotas to meet on getting cars out the door, they were not holding up many cars because there was a deviation from the norm. The X11 69Z car is rare occurrence , but many others smaller documented issues occurred during the production run. The main issue is these cars are a not "cookie cutter" type car with the many changes that took place, but when many readers see these books they are trying to restore their car thinking well this is the only way it could be done with this one part, because the book doesn't mention other parts or other cars that have different part numbers. I have seen a number of guys remove original parts from their car looking at Jerry's book thinking they were incorrect, to only find out later other cars built around there's to have those same parts they removed.
So to Pacecar, the Legends Manuals offer more info and a guide as the other books, but it really takes a lot of investigative work to pin down the right info on when a car was built and other similar time frame examples. the books are helpful, but still have a ways to go.
The R F stamps in Hoopers book was something that should not have been included. as Cook mentions no other examples have been found. As mentioned Vendors can sell anything, so don't trust them to get it right.