Not Camaro, but my 69 Corvair still had the original spiral shocks on it when I bought it. The car was built 12A (1968) and all 4 of the shocks were dated 6B68. A different format than the Camaro, but you can see the lag time (2nd week of June shocks on a 1st week of December car).
However, keep in mind that there were only 6000 Corvairs built in 1969, and I found dates all over the map for different things (carpet was November, 1968, gauge cluster was August, 1968, jack was September, 1968, etc...), so take this example with a grain of salt. The Corvair was at the end of its life cycle and cars were built approx 3 per hour off the line at Willow Run, so they were scrambling just to find enough parts to finish these cars!