26 C.F.R. § 1.1311(b)-1
Example: A taxpayer who keeps his books on the cash method erroneously included as income on his return for 1954 an item of accrued interest. After the period of limitations on refunds for 1954 had expired, the district director, on behalf of the Commissioner, proposed an adjustment for the year 1955 on the ground that the item of interest was received in 1955 and, therefore, was properly includible in gross income for that year. The taxpayer and the district director entered into an agreement which meets all of the requirements of § 1.1313(a)-4 and which determines that the interest item was includible in gross income for 1955. The Commissioner has maintained a position inconsistent with the inclusion of the interest item for 1954. As the determination (the agreement pursuant to § 1.1313(a)-4 ) adopted such inconsistent position, an adjustment is authorized for the year 1954.
Example: In the example in subparagraph (1) of this paragraph, assume that the Commissioner asserted a deficiency for 1955 based upon other items for that year but, in computing the net income upon which such deficiency was based, did not include the item of interest. The taxpayer appealed to the Tax Court and in his petition asserted that the interest item should be included in gross income for 1955. The Tax Court in 1960 included the item of interest in its redetermination of tax for the year 1955. In such case no adjustment would be authorized for 1954 as the taxpayer, and not the Commissioner, maintained a position inconsistent with the erroneous inclusion of the item of interest in the gross income of the taxpayer for that year.
Example: A taxpayer in his return for 1950 claimed and was allowed a deduction for a loss arising from a casualty. After the taxpayer had filed his return for 1951 and after the period of limitations upon the assessment of a deficiency for 1950 had expired, it was discovered that the loss actually occurred in 1951. The taxpayer, therefore, filed a claim for refund for the year 1951 based upon the allowance of a deduction for the loss in that year, and the claim was allowed by the Commissioner in 1955. The taxpayer thus has maintained a position inconsistent with the allowance of the deduction for 1950 by filing a claim for refund for 1951 based upon the same deduction. As the determination (the allowance of the claim for refund) adopts such inconsistent position, an adjustment is authorized for the year 1950.
Example: In the example in subparagraph (1) of this paragraph, assume that the taxpayer did not file a claim for refund for 1951 but the Commissioner issued a notice of deficiency for 1951 based upon other items. The taxpayer filed a petition with the Tax Court of the United States and the Commissioner in his answer voluntarily proposed the allowance for 1951 of a deduction for the loss previously allowed for 1950. The Tax Court took the deduction into account in its redetermination in 1955 of the tax for the year 1951. In such case no adjustment would be authorized for the year 1950 as the Commissioner, and not the taxpayer, has maintained a position inconsistent with the allowance of a deduction for the loss in that year.
26 C.F.R. §1.1311(b)-1