Retention of records.
Each manufacturer shall retain for a period of not less than 3 years all records required by this part, a copy of all claims and supporting data filed in support thereof, all commercial invoices or other documents evidencing taxpayment or tax-determination of domestic spirits, all documents evidencing taxpayment of imported spirits, and all bills of lading received which pertain to shipments of spirits. In addition, a copy of each formula submitted on TTB Form 5154.1 shall be retained at each factory where the formula is used, for not less than 3 years from the date of filing of the last claim for drawback under the formula. A copy of an approval to use an alternate method or procedure shall be retained as long as the manufacturer employs the method or procedure, and for 3 years thereafter. Further, the appropriate TTB officer may require these records, forms, and documents to be retained for an additional period of not more than 3 years in any case where he or she deems such retention to be necessary or advisable for protection of the revenue.