I have not tried the layering method for Clematis. Last year I lost three Clematis to some kind of fungal wilt. I removed all the dead material. I am happy to report that two of the three came back this year. Here is my list of Clematis
Clematis Abeline, new not planted yet
Clematis Anna Louise
Clematis Asao
Clematis Carnaby
Clematis Corinne
Clematis Dutchess of Albany
Clematis Erik Ruth
Clematis Gillian Blades, got wilt but returned
Clematis Niobe
Clematis Pink Champagne, first one died before I got it planted
Clematis Pink Champagne 'Kakaio'
Clematis Pink Mink, new not planted yet
Clematis Prince Philip
Clematis Rebecca
Clematis Red Star, new not planted yet
Clematis Sapphire Indigo, new not planted yet
Clematis Silver Moon
Clematis The President
Clematis Trikatrei
Clematis Empress, died from wilt
Clematis Jackmanii, from cutting