Article 56 clarifies the timing of deductions for taxpayers whose accounting periods do not align with the calendar year ending December 31st. Any deductible expenses or amounts (per Articles 54 and 55) incurred during the entity's specific accounting period are legally deemed to have been incurred during the tax year in which that accounting period concludes. This ensures that the expenses and the related income generated within that accounting cycle are matched and assessed together in the appropriate annual tax return, maintaining the integrity of the periodic assessment process.