No delays, mistakes, errors, or irregularities in any act or proceeding authorized or required by this chapter shall prejudice or invalidate any preliminary or final assessment, but may be remedied by subsequent filings, amending acts, or municipal, county, or board proceedings, as the case may require. When remedied, the preliminary or final assessment shall take effect retroactively as of the date of the original filing, act, or proceeding. If any final assessment made is set aside by any court or if for any reason the board determines it to be expedient to alter any final assessment, the appointing government may make a new assessment in accordance with this chapter.