It's a mint error in the sense that the mint used a very worn die to strike it. It's an error that's so common, that it will never add a premium to its face value.
How long does it take for a die to get that bad? Didn't they only mint each state quarter for a year?
Actually only for a few months since they have minted 5/6 a year since 1999. However, dies have a finite life. I recall reading that the life may only be a week or 2, depending on the throughput. As with any production process, it's a cost balancing act. At what point do you take the cost and downtime hit to change a die that has some minor visual concerns, but is still producing coins that are acceptable for commerce? (Hopefully someone has an actual reference for die life. I remember reading something like this on CT and am pretty sure this is a good ballpark figure, but hate to put it out there like it was a fact.)
I've always wondered that too. I assume quarters and nickels give the dies more of a beating than cents do.
In any case it woudn't be a "double" die. There's no such thing. Now it COULD be a doubleD die, but, unfortunately it ain't.
