Validity of assessment proceedings preserved when substantive conformity exists despite procedural defects, and service is upheld if acted upon. Section 160 provides that procedural mistakes, defects or omissions in assessments, reassessments, adjudications, reviews, revisions, appeals, rectifications, notices, summonses or other proceedings shall not, by themselves, invalidate those proceedings if they are in substance and effect in conformity with the intents, purposes and requirements of the Ordinance or any existing law, and that service of notices, orders or communications cannot be questioned if acted upon or not previously contested.