(a) Upon notice and hearing as provided for in the original assessment, or with the written consent of all affected landowners, the governing body may make supplemental assessments to correct omissions, errors or mistakes in the assessment relating to the total cost of the improvement.

(b) When an assessment, for any reason whatever, is set aside by a court of competent jurisdiction as to any lot, piece or parcel of land, 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, upon notice and hearing as provided for the original assessment or with the written consent of all affected landowners, may make a reassessment or a new assessment as to such lot, piece or parcel of land.