(a) Except for cases described in paragraph (b) of § 1.1312-3, no adjustment by way of a deficiency assessment shall be made, with respect to a related taxpayer, unless the relationship existed both at some time during the taxable year with respect to which the error was made and at the time the taxpayer with respect to whom the determination is made first maintained the inconsistent position with respect to the taxable year to which the determination relates. In the case of an adjustment by way of a deficiency assessment under the circumstance described in paragraph (b) of § 1.1312-3 (where the maintenance of an inconsistent position is not required), the relationship need exist only at some time during the taxable year in which the error was made.

(b) If the inconsistent position is maintained in a return, claim for refund, or petition (or amended petition) to the Tax Court of the United States for the taxable year in respect to which the determination is made, the requisite relationship must exist on the date of filing such document. If the inconsistent position is maintained in more than one of such documents, the requisite date is the date of filing of the document in which it was first maintained. If the inconsistent position was not thus maintained, then the relationship must exist on the date of the determination as, for example, where at the instance of the taxpayer a deduction is allowed, the right to which was not asserted in a return, claim for refund, or petition to the Tax Court, and a determination is effected by means of a closing agreement or an agreement under section 1313(a)(4).