If pidyon haben was performed late, must an additional fifth be added to the redemption payment?

This source-based Torah study examines the question: If pidyon haben was performed late, must an additional fifth be added to the redemption payment? The canonical Hebrew discussion develops the issue through the weekly Torah portion and the sources cited there, preserving the distinctions, tensions, and practical implications of the original text. This localized discovery layer does not add any new halakhic, medical, legal, scientific, historical, theological, or empirical ruling or claim beyond the canonical Hebrew source.