the mint missed a golden opportunity.

Had the U.S. mint kept track of their production of the coins in the double prosperity sets to make sure that they were indeed produced on 08 08 2008, then they would have had a compelling set to collect. Also by limiting the number of sets to that day's production, the set would have been made more desirable. The ideal way would be to over strike those coins with 08 08 2008. But that would have literally taken an act of Congress, if I'm correct, not to mention the cost of the machinery.

But all may not be lost. The mint probably kept detailed enough production records of their proof coins to know when they were produced, whether or not they will ever release that data...