When any street works to be executed under the private street works code have been completed, and the expenses of them ascertained, the proper officer of the council shall make a final apportionment by dividing the expenses in the same proportions as those in which the estimated expenses were divided in the original or amended provisional apportionment, as the case may be, and notice of the final apportionment shall be served on the owners of the premises affected by it.
The final apportionment, subject to any amendment made to it by a court on the hearing of objections to it under this section, is conclusive for all purposes.