I have a clematis twilight and noticed that two of the seed heads look light big wicker balls while the rest look completely different - is there a difference between pollinated and un-pollinated seed heads ?
Here are some great pictures of clematis seed. In the first picture, you see mainly "fluff" & one visible seed. Frequently the large flowered cultivars will only produce an occasional seed with LOTS of fluff!
When you see the seed , you'll know the difference.
Here is a link that might be useful: A Clematis forum link