If the actual cost of the improvements is substantially less than the estimated cost the assessment may be reduced proportionately on each parcel by recomputing it based on actual costs with the percentage and interest provided for in Section 9831 added thereto. The reapportionment or a statement that the assessment on each parcel has been reduced by a designated percentage shall be recorded in the same manner as the order levying the original assessment.
Installments of assessments levied on district-owned real property becoming due while the real property is still owned by the district shall be paid by the district. Conveyance of such real property into private ownership shall not release the lien thereon of the assessment and the unpaid installments of it.