The only thing I can extract from your question is this is Save our Homes for homestead property, where there is a 3% cap for tax assement which would be why taxes for property purchased in 2004 are alot less.
Regarding sales this year, I have seen this as of late where purchase price is less than assessed value. Today, even though selling price was $330k, the county uses their own formula for calculating taxable value. With short sales and foreclosures, one is buying property for less than its true value. So one should expect to have a taxable value reflect the true value of the property. Also, since they use closed sales as part of their formula, this is where mortgage fraud affects everyone. There is something one can do... The county begins their assessments in January and mails out tax statements to owners in August. At this point an owner can appeal their taxable value with the Value Adjustment Board at the tax assesor's office. Just make sure you have verfiable data to prove that their assessment is not accurate.
Just for the record... I don't agree with their method for calculating taxable values and not many people truly understand it. There seems to be some 'secret formula'. However, for those that are grandfathered-in, Save our Homes is truly wonderful.