Not sure if it is the same for Romans as it is for ancient Greek coins but I was walking around the museum at the original site of the olympics and they had some great coins which were in beter condition than most of the coins in my pocket now.
Apparently freshly minted coins make great offerings to the gods so you could get a coin in perfect newly struck condition being offered to the gods and thus never being in circulation. Knock down the temple to appease your new christian ruler and there it stays until someone goes treasure hunting.