The City Clerk shall, within 60 days after the completion of each local or special public improvement, compile the actual cost thereof and certify the same to the City Assessor, who shall adjust the special assessment roll to correspond therewith.
(A) Additional assessment. When any special assessment roll shall prove insufficient to meet the costs of the improvements for which it was made, the City Council may make an additional pro rata assessment.
(B) Refunds of assessments. Should the assessment prove larger than necessary by 5% or less, the same shall be reported to the City Council, which may place the excess in the city treasury or make a refund thereof pro rata according to assessment. If the assessment exceeds the amount necessary by more than 5%, the entire excess shall be credited to owners of property as shown by the city assessment roll upon which such assessment has been levied, pro rata according to assessment; provided however, that no refunds of special assessments may be made which impair or contravene the provisions of any outstanding obligation or bond secured in whole or part by such special assessment.