If, in the judgment of the Council, the varying benefits which are being derived by the several parcels of taxable property within an assessment district theretofore established by it, or in a zone thereof, or as to the extent of the areas of either, when the assessments are other than fixed lien assessments, either by reason of changed conditions or a reconsideration of original benefits the apportionment of which had been established by it, it may take proceedings to reestablish the apportionment of said benefits among said several parcels.
(Prior code App. A, § 154)