b5 differences thought the years?

Hey guys i was just looking over color charts for plymouth and noticed according to the ppg paint book, according to mymopar.com, it says the code for b5 blue is different from 69 and thoughout the 70s, i was wondering is the color actually a different 'hue'/shade or is there something i am missing something.

Thanks guys, btw lets see some b5 blue cars(prefer cuda) while your reading/ posting :lol: 8)