Our clematis are grown in 2 litre pots on 3 feet canes, (so around 3 feet tall) they are all 2 years old and fully hardy when sent out.
Our mail order boxes are 115cm tall, to allow for extra top growth in the height of summer. Also in late winter and early spring they may arrive much shorter (anything between 6 inches to 12 inches) if we have already pruned them back here on the nursery, this is perfectly normal for the time of year.