26 CFR 301.6501(j)-1: (j)-1 Investment credit carryback; taxable years ending after December 31, 1961.

With respect to taxable years ending after December 31, 1961, a deficiency attributable to the application to the taxpayer of an investment credit carryback may be assessed at any time before the expiration of the period within which a deficiency for the taxable year of the unused investment credit which results in such carryback may be assessed, or, with respect to any portion of an investment credit carryback from a taxable year attributable to a net operating loss or capital loss carryback from a subsequent taxable year, at any time before the expiration of the period within which a deficiency for such subsequent taxable year may be assessed. For purposes of this section a deficiency shall include a deficiency which may be assessed pursuant to the provisions of section 6213(b)(2), but only those arising with respect to applications for tentative carryback adjustments filed after November 2, 1966.