1. To correct omissions, errors or mistakes in the original assessment which relate to the total cost of an improvement, the governing body of the city or county may, without a notice or hearing, make supplemental or additional assessments on property within a neighborhood improvement district, except that such supplemental or additional assessments shall not, without a new election or new petition as provided in section 67.457, exceed twenty-five percent of the estimated cost of the improvement determined pursuant to section 67.457.
2. When an assessment is, for any reason whatever, set aside by a court of competent jurisdiction as to any property, or in the event the governing body finds that the assessment or any part thereof is excessive or determines on advice of counsel in writing that it is or may be invalid for any reason, the governing body may, upon notice and hearing as provided for the original assessment, make a reassessment or a new assessment as to such property.