Applicability of Rule 57F(4): non Modvat units need not maintain RG1 scrap records; collectors may request records as needed. Clarifies that Rule 57F(4) and its RG 1 scrap record requirements apply only to units that have opted into the Modvat Scheme; non Modvat assessees should not be routinely required to maintain Modvat specific records, although Collectors retain discretion to request records as necessary for accountal purposes.