quoting the first info page in the thread:
"This is a thread where us commuters can log our yearly commuting mileage in. Should be fun!"
Perhaps it should say to log you miles since the January start of 2009, rather than yearly commuting mileage, if that is the intention.
I joined the list in Oct 2009, and knew at that time my mileage for the previous 12 months. I put down that number, which matched my interpretation of what was asked for.