After a district is ordered established, if it is found that any parcel of land within its limits has been overlooked, or is not reported for assessment, or it is found that any owner or encumbrancer of any parcel of land has not been properly brought before the court, such mistake or order may be corrected. The county court shall order such parcel of land listed for assessment, and cause the owner thereof, and encumbrancer, if any, to be properly brought before the court by process or publication, and also any other owner or encumbrancer not already before the court. As to any such lands, or parties, the matter shall be proceeded with as if proceeded against in the beginning, and so as to enforce proper and proportional assessments. As to all other parties already before the court, the validity of the proceedings shall not be affected because some of the lands had been overlooked and some of the owners or encumbrances not brought before the court before the district was ordered established.