40 CFR § 86.079-31
Separate certification
June 9, 2020
Where possible a manufacturer should include in a single application for certification all vehicles (or engines) for which certification is required. A manufacturer may, however, choose to apply separately for certification of part of his product line. The selection of test vehicles (or test engines) and the computation of test results will be determined separately for each application.
[42 FR 45149, Sept. 8, 1977]