I suspect you read that in Appendix D: 1969 Camaro Trivia in Jerry MacNeish's 1969 Camaro book. It was one of my contributions. Way back in the '70s I started documenting '69s. No internet then so one communicated with other like-minded people via Hemmings Motor News and Old Cars Weekly. That's how I became acquainted with Warren Malkin, Jr. who was doing essentially the same thing on the East Coast. Still have all the stuff Warren sent over 40 years ago including two cars he was certain had been built with the yellow light AM/FM stereo. Both Z/28s; one 05A build, the other 05E. The comment in the book implies the change was made for the extended production run; we weren't certain at the time so that was what we went with.
The AIM copies that have been around now for over 40 years were not necessarily complete and may not have contained later updates. All hardcopy in those days; someone had to manually change out pages. Some details may have never been changed. Sometime during late February at both Norwood and Van Nuys, Chevrolet reversed the position of the horns, placing the high note horn on the passenger side. This is documented in original magazine photos. I have also noted it on several undisturbed, original cars. The Assembly Manual [Section 12 page A5] was never updated.
