I think for one, they are using a lot of korks. At the minimum I use 30, otherwise they can be flat. Also it looks like they have theirs trimmed into a really round ball, does that make sense? I bet they do use stiffener. Take my word for it, don't spray with stiffener before you bake, at least if you do, do it very lightly!! I had major disasters before!! LOL!! I don't use any kind of knot in the center. I'm by no means an expert, but this is how I do mine. I wrap the dowels with the ribbon and try not to leave any gaps when I wrap. I've found if I spray it with water before I bake they stay better too. Then I bake at 275 for 25 minutes. Then when I take them out I let them cool before I unwrap. Then be careful to unwrap, don't stretch them out too much. I try to loosen it on the dowel before hand. Then I measure before I cut everytime. Usually 2.5-3 inches depending on how big I need them. Then I sew them. I stack them on my needle and as it gets too full I push them down. I always use at least 30 or more. I run the thread thru several times and then tie off. I trim all ends to make it a full circle or ball, and then heat seal. Some ladies here use the woodburning tool, I've never tried it, but I'm going to soon, I'm sick of heat sealing!! Then I spray with Stiffy and hang upside down. That helps alot. Got that tip off here!! I hope this helps!!
Trimming is very important, I think. It really makes the korker look much fuller.