For the purpose of subparagraph (1) of this paragraph, amounts allocated by a cooperative association entitled to tax treatment under section 522 will be deemed allocated in fulfillment and satisfaction of a valid enforceable obligation, if made pursuant to provisions of the bylaws, articles of incorporation, or other contract, whereby the association is obligated to make such allocation after the retention of reasonable reserves and after payment of dividends on capital stock or other proprietary capital interests. Notwithstanding the provisions of subparagraphs (1) and (2) of this paragraph, amounts allocated as patronage dividends, refunds, or rebates during the taxable year, on or before the 15th day of the ninth month following the close of such year, with respect to patronage for years preceding the taxable year, shall be taken into account as an increase in its other cost of goods sold, or as a reduction in gross receipts, for the taxable year, as the case may be, where retention as reasonable reserves of the amounts so allocated beyond the year in which earned was proper in accordance with the provisions of section 521 and where the allocation is made to the patron on a patronage basis is proportion insofar as is practicable, to the amount of business done by such patrons during the taxable year or years in which the retained amounts were received by the cooperative association.
26 C.F.R. §1.522-3