Procedural defect immunity preserves proceedings when they conform in substance to statutory requirements and are acted upon. Proceedings such as assessment, re assessment, adjudication, review, revision, appeal, rectification, notices and summons shall not be invalid merely for procedural mistakes where they are, in substance and effect, in conformity with the Act; service of a notice, order or communication cannot be challenged if the recipient has acted on it or failed to contest service in earlier related proceedings.