As a developer in the GIS industry, a lot of our clients are County Assessors who use these appraisal systems on a daily basis in conjunction with GIS software to manage the physical land in their respective counties. I'm not in the least bit surprised by this.
These CAMA (computer assisted mass appraisal) systems are not only ridiculously overpriced, they are also hilariously outdated. How overpriced? Oh, they range anywhere from 500K to 1.5M. How outdated? Try green screens and as400. What you have is a small office of little blue haired Bettys entering data with no front-end or even back-end data validation going on. The market leaders for this software, such as Manatron, are just beginning to release SQL-based versions of this software. It's truly embarassing. Try hitting your county/twp appraiser's website and see how many spelling variations you can find of your own street. I think the record is about 37.
At least this property owner got an $800M value. In some cases the assessors can undervalue their buddies' commercial properties, meaning they will have to pay less taxes than the average property owner...a subtle display of corruption.