What is an unsecured property supplemental tax bill?

An unsecured supplemental assessment is an adjustment in real property valuation resulting from upward changes in assessed value due to changes in ownership or completion of new construction where the assessment is not a lien on real property. An unsecured property supplemental tax bill retroactively taxes the supplemental assessment of property on a pro-rata basis because of the Assessor's reappraisal of property at its full cash value on the date that a change in ownership occurs or new construction is completed.