Any labeling, advertisement, or other representation subject to this chapter which represents that any seed is certified seed or any class thereof shall be deemed to be false in this respect unless (a) it has been determined by a seed certifying agency that such seed conformed to standards of genetic purity and identity as to kind or variety, and is in compliance with the rules and regulations of such agency pertaining to such seed; and (b) the seed bears an official label issued for such seed by a seed certifying agency certifying that the seed is of a specified class and a specified kind or variety. Seed of a variety for which a certificate of plant variety protection under the Plant Variety Protection Act [7 U.S.C. 2321 et seq.] specifies sale only as a class of certified seed shall be certified only when