I think there was a reason for the period, because they did it for multiple years, even into 1992 when the format of the card back entirely changed. But I don't think it was a way to generate interest in the product. That would definitely be a stupid way to do that. My best guess is that it was an internal thing for tracking or QC purposes. Say for example they did have two different production facilities. If Donruss people open packs and find substandard cards, they know which facility the cards came from by looking for the period. Same theory could apply to the *Denotes versus *Denotes* error. This with the period could identify 4 different printing lines.