I've taken many clematis cuttings in the spring, usually always just a single node buried deep with leaves sticking out, and in the first year the nice roots will form but often no more (or not much) top growth. It's the next year that I'll see lots of growth from those roots. In the fall dormant season is the best time to pull them apart and plant them out in the landscape nice and deep (top bud beneath the soil is okay!), but they live over the winter still in my propagation jugs outside just fine as well.
I have noticed with clematis, though, that if you have a piece of stem between where the roots are forming and the lowest bud/node of the plant... that piece of stem is often pretty fragile. If it breaks, suddenly the roots have no bud to grow from, and I don't think they can make another from the internode that remains. So I recommend making sure that lowest node is planted deeply enough to get roots of its own (so such a problem doesn't occur),
Congratulations on your success!