As far as I'm aware there is NO JS23 in 1972.
1972 Challenger 318 = 15,175 I'm pretty positive but someone prove me wrong as I don't want you thinkingbhese are correct until someonne else concours.
These numbers were never kept by Chrysler, the numbers are close estimates. The sad thin is if we ever want to know exactly how many cars were built with what for an example:
1970 Plum Crazy 340 Cuda A/C, 6-Way seat, Vinly Seats, Rallye cluster etc
We'd have to get every 1970 340 Cuda next to each other in a big field go through each cars options then brake them down from there......so as you can see it's highly unlikly we'll ever know the true figure of cars made.
It's easy when there are 1 of 1 cars or 5 of 5 etc becuase the are usaully counted for and probably have all bee in the same car park.
Hope this helps in some way......