If, after final settlement with the contractor for any improvement and after full payment of all vouchers or bonds except those bonds and interest coupons not presented for payment, although called and for which funds are available and reserved, within the period of time specified in Section 9-1-5, issued on account of that improvement, there is any surplus remaining in the special assessment or special tax above the specified payments and above the amount necessary for the payment of interest on those vouchers or bonds, such surplus shall be applied to reimbursing the public benefit fund for any amounts paid from such fund on account of the improvement. If, after the public benefit fund has been reimbursed, a surplus still remains, the proper authorities of the municipality shall declare at once a rebate upon each lot, block, tract, or parcel of land assessed, of its pro rata proportion of that surplus. Such rebate shall be paid to the owner of record of each such lot, block, tract, or parcel at the time of the declaration of the rebate. Should any additional funds be collected after the original rebate is declared, the municipality shall not be required to declare a supplemental rebate for 5 years from the date the original rebate is declared. The municipality may deduct for its cost and expenses for declaring and making any rebate not more than 5% of the amount declared to be rebated. The board of local improvements shall keep and exhibit publicly in its office, an index of all warrants upon which rebates are due and payable and upon proper proof, the warrants shall be repaid to the persons entitled thereto.
     However, whenever any municipality having a population of 500,000 or more has appropriated or set aside a fund sufficient in amount to meet all estimated deficiencies in interest, cost of making, levying, and collecting a special assessment or special tax, and of letting and executing contracts, advertising, clerical hire, engineering and inspection, court costs and fees of commissioners in condemnation proceedings incurred in such a proceeding and has provided, in the ordinance providing for the assessment, that a certain sum not to exceed 5% of the amount of the assessment or special tax shall be applied toward the payment of the specified and other costs of making and collecting the assessment, the money collected in the fund created by this 5% so added as hereinbefore authorized shall be used to pay all deficiency in interest in the warrant, and the balance shall be used to reimburse the corporate funds for advances made from the corporate funds on account of costs of the special assessment or special tax or other expenses of the improvement for which the special assessment or special tax was levied.