Article 143 bis provides a 'Deemed Assessment' mechanism to speed up tax finalization. If the Tax Authority does not issue a formal assessment within the statutory time limit (defined in Article 147), the taxable income or loss declared by the taxpayer in their original return is legally considered the final assessment. This ensures that taxpayers are not left in indefinite limbo. However, this deemed status remains subject to the Authority's rights to later rectify, revise, or perform additional assessments under the rules of Articles 148 and 149 if errors or omissions are eventually found.