Is the free annual credit report based on a calendar year?

I know you get a free report from the big three every year. Is this based on a calendar year or contingency?

For example, if I ordered all three on 11/22/2008...could I hypothetically order all three again on 1/1/2009? Or would I not be able to order them again until 11/22/2009?

Thanks for the help.
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