It is hard enough to figure out the correct taxable value of the land and buildings when you have examples being sold in the same area on a regular basis to bass the value off of. But when no land has changed hands in decades and the structures on decades old deciding what part of the $400,000 sales value is the land vs the building is impossible, You are going to end up in court ALL the time.
And you have not explained how to handle the two extremes.
Assuming a building burns down and the property is sold. First time property is sold (without buildings) in 30 years so we are setting the first true market value of property in decades.
Then you get two extreme possibilities (and a ton more between the extremes)
1) The property is in a very popular area and sells for 10 times It assessed value. Next years taxes on everyone in the area just went from $1,000 to $10,000 and you just bankrupt a hundred families.
The other extreme
2) the property sells for 1/100 of assessed value. The following year the City budget drops from $10,000,000 to $100,000 and the City goes bankrupt.