The notion of rare dimes and a bicentennial quarter being worth $72 million each and still circulating is highly improbable.
While there are indeed rare coins that can fetch high prices among collectors, such as certain misprinted or limited edition coins, a valuation of $72 million each would be unprecedented in the world of numismatics (coin collecting).
Rare coins typically gain their value from factors such as their historical significance, rarity, condition, and demand among collectors.
While some coins can indeed be worth significant sums, values in the millions are exceptionally rare and usually associated with coins that are either extremely rare or possess some unique historical significance.
Furthermore, if such coins were still in circulation, it's highly unlikely they would go unnoticed given the attention and scrutiny that rare coins receive from collectors, enthusiasts, and even professional numismatists.
If you're interested in rare coins or have come across something you believe to be valuable, it's always a good idea to consult with a reputable coin dealer or professional appraiser who can provide accurate information and valuation.