Only the species clematis will come true from seed and that is only if they are self pollinated. None of the hybrids come true from seed. The seedlings may look a lot like the parents or they may be something not yet seen.

large flowered ones take a year or so to germinate.... not that they won't just takes forever and you have to wait another few years to see what they look like...
herbaceous and species will be easier to grow and most of them will come true to parent. I have stunning Bill Mckenzie growing in my neighbour's garden grown from seed and my clematis viorna bloomed first year climbing over jap maple. I have multiple herbaceuos clems which a delight for fall garden...

lindalana, I really like the Viorna, it is georgeous. You said it bloomed the first yr from seed? I have Ramona,Henryi, and another double white I cant remember offhand. Loved Ramona's bright blue/lavender blooms. I havent heard the term herbacious clems. Whats the difference? I do have some seeds from Radar Love that I recieved with an Ebay purchase,that I was thinking of trying next yr.Are they similar to your Bill Mckenzie ?
Tammy

Herbaceous clematis die completely back to the ground in winter, leaving no above-ground 'trunks' or vining stems. These would include species like C. recta, heracleifolia and the straight integrifolia.

Technically, one cannot call (and therefore sell seeds so named) the seedling of a named cultivar of clematis as that cultivar. The seeds of 'Radar Love' will just generate other seedling tanguticas. They may or may not look exactly like the parent plant and cannot be called by that name. What I am trying to say very awkwardly is that named forms of any plant are not seed grown - they MUST be propagated by asexual means....division, cuttings, layering, grafting, etc.

I understand what your saying gardengal. Similar with roses. I had been hesitant to try other types of clems, such as tangutica, because I thought I read they can be invasive.
Tammy