Procedural defects in tax proceedings don't invalidate actions if they conform to statutory intent and are acted upon. Section 160 preserves validity of tax proceedings despite mistakes, defects or omissions where such proceedings are in substance and effect in conformity with the intents, purposes and requirements of the Act or any existing law, and protects service of notices, orders or communications from being questioned where the recipient has acted on them or failed to challenge service in earlier related proceedings.