1. To correct omissions, errors, or mistakes in the original assessment that relate to the total cost of an improvement, the governing body of the district may, without a notice or hearing, make supplemental or additional assessments on property within a sanitary sewer improvement area, except that such supplemental or additional assessments shall not, without a new petition as provided in sections 204.650 to 204.672, exceed twenty-five percent of the estimated cost of the improvement as set forth in the petition under the provisions of sections 204.650 to 204.672.

2. When an assessment is, for any reason whatsoever, 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.