(A)   The 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 Assessor, who shall adjust the special assessment roll to correspond therewith.
   (B)   Should the assessment prove larger than necessary by less than 5%, 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 the assessment.  No refunds of special assessments may be made which impair or contravene the provisions of any outstanding obligation or bond secured, in whole or in part, by the special assessments.  In the case of assessments due in installments, the Council may order the refund given by credit against the installments last coming due.
   (C)   When any special assessment roll shall prove insufficient to meet the cost of the improvement for which it was made, the Council may make an additional pro rata assessment, but the total amount assessed against any one parcel of land shall not exceed the benefits received by the lot or parcel of land.