property tax

We bought our home in beginning of 2000. In 2002, the home price dropped. Therefore, the county office reduced assessed value by 20%. The county office said it is temporary. However, the county keeps another property value by adding up 2% each year. This year, 2005, the county office sent a notice of the assessed value of theOriginalBoughtPrice*1.02**5 (* is times, ** is power). I feel it is not fare, because:

1. The county office agreed the fair market value of my home in 2002 was 20% off the purchase price, and later adds on value should be subject to proposition 13 with 2% limitation based on the reduced price.
2. During recession period, between 2001 to 2004(?), when the home price was dropped, how could the office keep adding 2% of value to the price when we purchase?

Anyone could give me some advice if I could argue with the county office and how to do so if yes. Your helps are greatly appreciated.