Couple of comments on this thread.
TCAD's rolling its values YOY is a huge long-term boon for them.
No need to apply resources on appraisers or researchers for the past 12 months.
No need to apply resources on protests
Tax rolls will increase due to "assessed value" increases
Most protest aggregators will be put out of business (as noted earlier)
TCAD (and other appraisal districts) will change land/improvement value when the improvement valuation exceeds cost to replace the structure by a certain amount. If I recall correctly, it was 1.2x in Travis a few years ago. It typically is revisited based on the status for an entire entire neighborhood.
TCAD has a fairly decent search feature and, with it, you can download CSV files based on your search criteria. The CSV can be read into Excel or parsed using some fairly straightforward code. I downloaded information from 2018, 2019, and 2020 for 2 zip codes in Travis county and found the following:
2018 -> 2019 valuation changes for all homes
16.5% decreased
3.7% no change
79.9% increase
13.5% increase by more than 10%
Over 7% turnover on ownership
2019 -> 2020 valuation changes for all homes
0.4% decreased
92.8% no change
2.8% increase
0.8% increase by more than 10%
Over 5% turnover on ownership
My homestead was one that increased by more than 10%. My home was the only home in the neighborhood to change value and 3 homes sold in 2019. In fact, one of them sold for 20% more than 2019 valuation and retained its 2019 valuation.
I called TCAD and an appraiser called me back. He told me that a functional obsolescence factor (agreed to in a 2015 formal hearing) had been removed from my valuation. This was capricious and indefensible, but it is up to me to defend, of course. Sigh....