Files of vouchers and purchase orders shall be maintained by serial number with the most recent number being placed on top. If an additional set is maintained, such additional set should be maintained in alphabetical order by name of vendor. Ledgers shall be kept by account number. All other special purpose items shall be kept as required for easy and frequent reference.
N.Y. Comp. Codes R. & Regs. Tit. 9 §§ 1625-6.4