The total assessed valuation can go up if new construction brings in more taxable property. It can go down if buildings are taken off the tax rolls, such as in the case of the swing school that was formerly an office building. New construction of schools does not add to the overall total because they are tax-exempt. Most of the new Park-Madison governmental office building downtown is tax-exempt, but the stores and commercial offices are new ratables. If a house is demolished, the city can only assess taxes on the vacant land. Tax appeals can be used to reduce the taxable value of a building.
These are some of the variables in determining the total assessed valuation. Obviously homes and other property can increase in value over the years. Sorry for any confusion.