It depends entirely on when the miles were flown. While the program year is valid from March 1st through the following February, qualifying is based on the calendar year.
It's the statement that you made silver in January that confused me. Since your preferred miles balance resets to zero on January 1, you must have made silver prior to that. Maybe the system didn't update your status until January which is possible.
So, since January 1st, if you've flown 37K miles, you've earned silver through 2009 and the following program year, ending 2/28/2011. Get to gold if you are able to and it's worth it to you to get it. Earlier upgrades and *G lounge access when traveling internationally are the biggest reasons to have it.