If you are finding the date on a flap that folds into the carton the printer would have been the one to have done that as most customers do not spec dates on the outside of the carton. Often printers put info including registration marks and color bars on glue seams where they are not visible unless you rip apart the package.
I sold paperboard rolls and sheets to Folding Carton Plants, as a matter of fact Flashfold Carton (2nd photo) was a customer of mine so this is first hand info.
the 2 cartons below are for 70-73 Z28 Bowtie centercaps
The original type raised logo NOS caps came from the 84 dated carton and the later style from the 89 dated carton.