(a) Information to be supplied by beneficiary—(1) In general. The beneficiary must supply the information required by subparagraph (3) of this paragraph for any prior taxable year for which a recomputation is required under either the exact method or the short-cut method. Such information shall be filed with the beneficiary's return for the year in which the tax under section 668(a)(2) is imposed.

(2) Failure to furnish. If the beneficiary fails to furnish the information required by this paragraph for any prior year involved in the exact method, he may not use such method and the tax computed under paragraph (c) of § 1.668(b)-1A (the short-cut method) shall be deemed to be the amount of partial tax imposed by section 668(a)(2). See, however, paragraph (b) of this section for an exception to this rule where the short-cut method is not permitted. If he cannot furnish the information required for a prior year involved in the short-cut method, such year will be recomputed on the basis of the best information available.

(3) Information required. The beneficiary shall file the following items with his income tax return for the taxable year in which the accumulation distribution is included in income:

(i) A statement showing the gross income, adjustments, deductions, credits, taxes paid, and computations for each of his taxable years for which a computation is required under the method by which he computes his partial tax imposed by section 668(a)(2). Such statement shall include such amounts for the taxable year as adjusted by any events subsequent to such year, such as any adjustment resulting from the determination of a deficiency or an overpayment, or from a court action regarding the tax.

(ii) A copy of the statement required by this subparagraph to be furnished by the beneficiary for any prior taxable year in which an accumulation distribution was received by him which was also deemed distributed in whole or in part in the prior taxable year for which the statement under subdivision (i) of this subparagraph is required.

(iii) A copy of any statements furnished the beneficiary by the trustee (such as schedules E and J of Form 1041, etc.) with regard to the current taxable year or any prior taxable year for which a statement is furnished under subdivision (i) of this subparagraph.

(b) Exception. If by reason of § 1.668(b)-1A(e) the beneficiary may not compute the partial tax on the accumulation distribution under § 1.668(b)-1A(c) (the short-cut method), the provisions of subparagraph (2) of paragraph (a) of this section shall not apply. In such case, if the beneficiary fails to provide the information required by subparagraph (3) of paragraph (a) of this section for any prior taxable year, the district director shall, by utilizing whatever information is available to him (including information supplied by the beneficiary), determine the beneficiary's income and related expenses for such prior taxable year.

(c) Records to be supplied by the beneficiary—(1) Year when return was filed. If the beneficiary filed an income tax return for a taxable year for which a recomputation is necessary, and the period of limitations on assessment under section 6501 for such year has expired as of the filing of the return for the year in which the accumulation distribution was made, then a copy of such return, plus proof of any changes of liability for such year due to the determination of a deficiency or an overpayment, court action, etc., shall, to the extent they verify the statements required under paragraph (a) of this section, serve as proof of such statements. If the period of limitations on assessment under section 6501 for a prior taxable year has not expired as of the filing of the beneficiary's return for the year in which the accumulation distribution was received, then the records required by section 6001 to be retained by the beneficiary for such prior taxable year shall serve as the basis of proof of the statements required to be filed under paragraph (a) of this section.

(2) Year for which no return was filed. If the beneficiary did not file a return for a taxable year for which a recomputation is necessary, he shall be deemed to have had in such year, in the absence of proof to the contrary, gross income in the amount equal to the maximum amount of gross income that he could have received without having had to file a return under section 6012 for such year.

(3) Distributions deemed averaged. In order for a beneficiary to use income averaging with respect to a prior taxable year (see § 1.668(b)-3A(c)), he must furnish all the information that would support the computation under section 1301 as if the distribution were actually received and averaged in such prior taxable year, even if a portion of the information relates to years in which no amount was deemed distributed to the beneficiary.