Filing of Form 67 as specified in Rule 128(9) is directory in nature and provisions of Rule 128 cannot override the provisions of DTAA.
Background:
Section 90 of the Income Tax Act, 1961 provides that the Central Government may enter into agreement with Government any country or territory outside India to eliminate double taxation of income.
In this regard, Article 25 of DTAA provides mechanism for elimination of double taxation by way of allowing credit of tax paid in other country against the tax payable in India (in most cases).
In order to streamline the process of claiming of credit under DTAA, Government of India has incorporated Rule 128 into the Income Tax Rules, 1962. Rule 128 states that in order to claim foreign tax credit, assessee is required to file Form 67 on or before the due date specified for filing return of income under section 139 (1).