Yellow Rack Header Cards

PaulMaul

So I notice that there are two versions of the yellow rack pack header card used from 1970-1973. One version only has the printing on one side with the reverse blank. The other version has the same "54 cards for 39 cents" writing on both sides. Is there any definitive info on which releases each was used for? The one-sided version seems to have been used for 1971 baseball, but many images show 1970 racks with the two-sided version. Moreover, they both have the same code number. Anyone have more details? Stuff like this is great for checking for legitimacy.