Answer: Most perennials (flower plants that die back to the ground each winter and regrow from the roots in spring) as a rule are cut back to the ground in the fall after frost has literally killed the stems and foliage. The purpose of doing this is to remove the dead material that will not grow again; it can be done in the early spring if you missed doing it in the fall.
Clematis however is a hardy vine and most types do not die back all the way, as you have seen. So it is treated a bit differently.
Depending on what particular kind of clematis you have you might prune it back every spring to about 18 inches, or you might prune off only winter killed tips of the vine, or you might wait and prune it after it blooms.
Since it sounds like yours is doing great I would not change a thing -- but if you want to read up on clematis and pruning them, here is some information.
You may need to cut and paste the complete url into your browser. I hope this helps clarify. Enjoy your clematis!
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