What Rob often does, especially with some of the rarer stuff, is grows a bunch of them from seed, and puts some of the seed into tissue culture. The seed-grown plants, not being divided and divided in vitro, reach maturity earlier. The seed grown plants are the first to be sold and then later the tissue cultured plants are released. Seed-grown material is more highly sought after because each plant is a unique individual, whereas tissue cultured plants share their genes with thousands of other clones.
So whenever you see a reference to different individuals from seed on his pricelist, it means they're from seed and not TC. If you seed 'selection from 42 clones' or something like that, it means they are from tissue culture.
In relation to the jacquelineae x izumiae, my understanding is that the hybrid appeared amongst seed-grown plants. Occasionally a hybrid will appear in TC, but Sods Law mitigates against that. When Rob released a bunch of seed-grown lowii, some of them turned out to be Trusmadiensis. Of course, none of their siblings in TC turned out to be the hybrid, they were all pure lowii.