Huw , you may want to check Abf and contact the knifemakers near you who do folders etc . They will have better idea
I was recently at my parents place, and after there recent move they came across a folding knife that belonged to my Mums grandfather.
It is pretty
Mostly because they didn't have anything better or readily available than those. You can say the same thing about Dexter-Russell's as well, they don't