Taxes are based on the assessed value. In NC, statute requires jurisdictions to revalue once every 8 years at a minimum. Most do them in 4 year intervals. At the beginning of the reval period, houses are assessed higher than actual value but by the end of the period, it is below. It evens out the valuation over the period of time between revals.
Topic, this house should have had at least two kitchens taken out and converted to bedrooms or additional family areas. You can see the Duggar handiwork throughout. And...is that supposed to be a water feature in the picture of the staircase (there's a pit in the floor next to the bottom of the stairs)?