https://www.merriam-webster.com/dictionary/overassessment
OVERASSESSMENT Definition & Meaning - Merriam-Webster
The meaning of OVERASSESSMENT is the act or an instance of assessing something (such as a property) at too high a rate, amount, or value : improperly high...
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https://www.irs.gov/irm/part4/irm_04-023-011
4.23.11 Prompt Action in Tax Underpayment and Overassessment Cases | Internal Revenue Service