I thought people had to REQUEST a reassessment. We did this for our old house (purchased in 2006, asked for reassessment in 2009) and it was granted to us after we filled out a short application including a few recent sales comps.
But I had no idea that the county would just send someone a letter saying, “your house has droped in value and now you owe less.” I wonder if this varies between the city and the county assessors?