(iii)any such debt or part of debt may be deducted if it has already been written off as irrecoverable in the accounts of an earlier previous year [(being a previous year relevant to the assessment year commencing on the 1st day of April, 1988, or any earlier assessment year)] [ Inserted by Act 4 of 1988, Section 11 (w.e.f. 1.4.1989).] but the [Assessing Officer] [ Substituted by Act 4 of 1988, Section 2, for " Income-tax Officer" (w.e.f. 1.4.1988).] had not allowed it to be deducted on the ground that it had not been established to have become a bad debt in that year;