I was recently acquired a 2001 Uncirculated Philadelphia Coin Set. There were two NY Quarters in the coin set and it was missing a NC Quarter. There does not seem to have been any tampering with the coin set. Could this have been an error from the mint and if so how common would this be. Any feed back would be greatly appreciated. I have been out of the coin collecting for a while and recently have been trying to get back into it.