In case any parcel of land against which any assessment has been levied has been subdivided or partitioned among several owners thereof, said Director of Public Works, on the written application of any owner thereof, shall make a proportionate division of such assessment and may amend the original assessment by a proportionate distribution of the assessment upon the several subdivisions of the parcel of land originally described. Such proportionate division of an assessment shall be without prejudice to the contractor or his assigns as to any assessment made in pursuance of the provisions of this Article. Such amended assessment shall bear date the same as the original assessment.