Validity of assessment proceedings preserved despite procedural defects; acts in substance conforming to statutory intents remain effective.

Proceedings under the Act, including assessment, re assessment, adjudication, review, revision, appeal, rectification and issuance of notices or summonses, shall not be invalid merely for mistakes, defects or omissions if they are in substance and effect in conformity with the intents, purposes and requirements of the Act or any existing law. Service of a notice, order or communication cannot be questioned where the recipient has acted on it or failed to challenge service in earlier related proceedings.

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