When is the market value assessment for property taxes determined?

After I wrote my last post about my concern about the market value of our house, I asked my aunt who is an appraiser when the values are determined. She says that the values are assessed every January and they are based on the sales from the previous year. So if I understand her correctly, the 2013 market value was determined by the 2011 sales. So that's a relief that the $40,000 drop in value is not necessarily a prediction of a further decline in value this year.  I also found a website for a different county that says:

The value notice for payable 2013 tax is based on:
The market value of each property on January 2, 2012. The January 2, 2012, market value was based on "open-market-sales" that happened between October 1, 2010 and September 30, 2011.

I'm starting to wonder if Eppraisal is actually more accurate than Zillow?  On September 17, 2011 Eppraisal valued our house at $165,161 and that falls at the end of the date range that the county used to determine our house's value.  The value our county came up with was $167,200, which is pretty close.

By the way, here is what Eppraisal came up for the value today:

The exact same value! I wonder how often they update the values on that site? However, the Zillow value has decreased since September.

So, I don't really have any conclusions other than it looks like our tax assessment uses somewhat outdated sales information.  I guess I'll have to wait until next year to see if it drops further.

I really had not planned on moving out of our house any time soon, but my husband came home from work the other day saying he wants to start looking for a job in his home town.  I hate to wish him ill-luck, but I hope he doesn't find anything too soon so our house value can bounce back up.  The houses in his home town were not as dramatically affected by the down housing market, so it wouldn't be like we'd get a great deal if we bought a new house there.