Substantial compliance preserves tax proceedings despite procedural defects when actions conform with statutory intent.

Provision preserves validity of assessments, adjudications, appeals, notices and related tax proceedings despite mistakes, defects or omissions if they are in substance and effect consistent with the intents and requirements of the Act or any existing law; similarly, service of notices, orders or communications cannot be questioned when they have been acted upon or were not contested in earlier related proceedings.

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