I don't think their was a set rule. It depended on what was ordered and if the parts were available to build. My 71 Charger R/T Hemi was the first in a series of 6 consecutive serial # Hemi cars ordered by the same dealer. The cars were all low option other than the Hemi engine, they were ordered at the same time and were built in series. I have the NHOA list of known serial #'s and there is no set pattern.
