All Clematis, especially the type II large flowered hybrids take several years to mature.

Pruning encourages new growth which encourages buds.

I don't grow Nelly, but in my experience second year plants are still busy growing roots. This seems to be true whether I plant them as tiny first year plants or as second year plants. I get my first blooms on third year plants usually, in the range of about 15 or 20 blossoms, and in succeeding years I get more each year. The only plant I've had bloom the first year in the ground was one that was a couple of gallon pot, not sure how old it was then. Clematis are wonderful plants, but require patience.

Adequate moisture is important, "cool feet" aren't, so your mulch is perfect to keep moisture levels even.

esther_b, I have a 4th year Josephine that I only got one bloom on this year! One measily bloom! I have chopped her till heck won't have it all the previous years. Could be because I did chop her last summer.
She's got lots of green growth and looks great but one bloom!
You are not alone lol. :)

Josephine has not been a heavy bloomer for me. Mine is at least five years old and had twelve flowers....I'm not impressed. Mine is in full sun as recommended and has been hard pruned and also left unpruned. Still doesn't do much...

well I am glad to hear someone else has a problem with nelly!! Mine has been in the same place for over 7 or 8 years. I have amended the soil and get great looking plant with no blooms. the first few years I did get some nice blooms but never very many. I am thinking it is time for a change in her location.