You earned Silver (FO) for 2012. When this happened, DL gave you FO immediately, even though you really did not earn it until next year. So your present FO status is really '12.

You earn miles on the calendar year. They give you status for the next year, but that ends after Feb (for all).

So you are silver until Feb 2013.

As to rollover. Any MQMs you have over 25k as of 12/31/11 will carry over into '12/ This will be your starting balance for that year.