Sure, plants were and are sometimes propagated by seeds, but that doesn’t have much direct relevance in this case, except that we might not have hybrids like the Damasks or the Noisettes if it weren’t for occasional human seed propagation and seedling selection events. The written history of the musk rose in Western Europe and its colonies suggests a genetically narrow initial introduction before the year 1600, and the true species was even nearly lost for a time before its relatively recent rediscovery in old gardens and cemeteries on both sides of the Atlantic. Most likely any seedlings of an isolated clone of a foreign diploid species that were not substantially true-to-type would either have been renamed if they had value or discarded if they were inferior, and if seedling events were common and the genetic base were wide, there would probably be significant diversity detected in the extant cultivated material today.
Luckily, researchers can compare DNA samples of extant R. moschata clones with one another along with their historic hybrids and learn much more, and they have. The clones of R. moschata tested in the Florida study included the one from Graham Thomas, which he had rediscovered at the home of E. A. Bowles, and two others also found growing in England. Since the species had gone out of favor (and even became confused with R. brunonii) and become rare in gardens for so many decades, these lately rediscovered remnants had extra significance–they were relics of a bygone era, one probably also much closer to the time the species was first officially named in 1762. It matters that the rediscovered R. moschata has been demonstrated to be the likely parent of ‘Champneys’ Pink Cluster’, one of the main reasons we are even talking about musk roses right now. The R. moschata clone that was found by Iwata et al. to be closest to the species origins of the ancient Damask rose (‘Kazanlik’, ‘Autumn Damask’, ‘York and Lancaster’, and ‘Quatre Saisons Blanc Mousseux’, which were themselves genetically indistinguishable) differed only slightly (one base pair) from the double musk rose that they tested, so while the parent clone of the Damask and the double musk might not be completely identical clones, they are still very nearly identical. I also don’t believe that no one ever raised Damask roses from seed, or credibly claimed that it wasn’t and couldn’t be done–it’s obvious that there would not be the overall diversity of clones today otherwise. It’s only true that various early Damask clones did indeed arise as sports, including the four that were found to have nearly identical DNA sequences in the Iwata et al. study: ‘Autumn Damask’, ‘York and Lancaster’, ‘Quatre Saisons Blanc Mousseux’, and ‘Kazanlik’. Whether additional Damask cultivars arose from seed or from sporting events, all true Damask roses must still share the same species ancestors, now understood to be R. moschata, R. gallica, and R. fedtschenkoana. If any rose contain more or fewer species than the type of the species, given this realization, then taxonomically, it doesn’t actually belong in R. x damascena. It’s something else.
It seems that there is still some fixation on references earlier (1728) than Herrmann’s, but that is largely irrelevant to the identity of the species. Hermann did include the single musk in his treatment, by the way–he lists “R. moschata minor, flore simplici” as included in his species concept, and simply says that he had not seen the single form (“Simplicem non vidi.”) It is implied that the single musk was only expected to differ meaningfully in the number of petals, or some other minor trait or traits. The precise clone that might have served as the model of R. moschata is also somewhat tangential to its overall identity at this point, again because we are discussing a species and not a cultivar (but, I would ask, why would this supposed shining-leaved musk rose that everyone was talking about have disappeared from cultivation, while the matte-leaved variety has persisted in such far-flung regions of the world? Does the existence or nonexistence of a glossy-leaved musk rose even meaningfully change the rest of the story?). If a glossy-leaved clone of R. moschata ever existed, there is certainly no widespread physical evidence of it now, and it doubtfully played any serious role in the background of important hybrids like the Noisettes or Damasks, given the DNA results. Its known hybrids are not exactly glossy-leaved themselves, so the trait (if it ever existed) clearly didn’t impact them meaningfully. We don’t know for certain that Bradley in 1728 was even talking about the same species as Herrmann, either. It would be a familiar kind of origin for a myth, though: all it takes is one person to write about a glossy-leaved musk rose, and countless others will repeat the earlier reference without even having seen the plant described.