Record retention period requires registered persons to keep GST books for the statutory term, extended when appeals or investigations exist. Registered persons must retain books of account and other records under section 35 for the statutory baseline retention period measured from the due date for filing the relevant annual return. If the person is party to appeal, revision, proceeding or investigation under the Act, records pertaining to that subject matter must be retained for the period that is later: the post disposal retention interval after final disposal, or the baseline statutory retention period.