Thanks for the details, OC Richard! Your pictures give me good details and clues towards a construction process.

The pictures indicate that the hair can get folded over at their tops, which strikes me as a solid means for attaching them securely, at least vs attaching them straight. I remember seeing this technique in instruction for making modern-style hair extensions, and while I liked its prospects for reliability (hair has to break in order to fall off), I was worried that it might not be possible given how thick horse hair is (compared to human hair). The pictures you posted indicate that it is possible, and that I shouldn't readily discard the idea (which I had been considering for a Version-1.0 sporran).

Another thing the picture seems to indicate is that the hair-body consists of several smaller bundles, which I presume could get made in advance of being attached (to the sporran's main body), and which conceptually sounds easier to stitch-down than trying to work with unbundled hair.