In the account, the names and addresses of purchasers need not be given. Where a commission merchant has entered into a contract with two or more producers or consignors which contract provides that the returns for farm products sold for the account of such producers or consignors shall be pooled on a definite basis as to size or grade, or both, during a certain period of time, then a commission merchant shall obtain the written consent of the consignors and shall be required to render an account of sales, showing the net average pool return on each size or grade, or both, from sales made and shall keep a correct record of such sales, showing in detail all information as required in Section 56271.