** Am I legally required to tell them they have not assessed my property?**
You are not legally required to tell them they have not assessed your property. However, they can tax you for omitted property for the current year and four prior years. If you do not correct the error, you need to be prepared to pay the current year’s taxes and taxes for prior years. Visit:- https://www.poconnor.com/texas-property-tax-less-faqs/ for more on Texas property tax exemptions.