A couple of thoughts on the topic. Helmets like this had inner padding to cushion blows. Now, I think that to affix such a lining there are only so many reasonable ways to go about it. I think that the decorations in the felt covered helm are fancy rivet heads that take the terminal of the thing that attaches the lining and makes it decorative.
Here are some outline drawings of helmets of this class, more or less, and the arrangement of holes on them.
This is from Grancsay's article on Barbutes in the Bulletin of the Met.
