I think what you are showing there is actually the result of poorly maintained tooling for the "blanking out" process during manufature of the ring, not something that has developed over time.
It's a common feature when blanking high strength light alloy components if the punch to die clearance...
Hi, I've got these that you can have for £25 plus postage if they're good enough, the clip is nice - the nut not so but has good threads. Definately 31/32" x 30TPI.
Very hard to find as you probably already know.
It'd be nice to think these unidentified forks in my parts bin were by Gios, but don't think they would have made any with mudguard mounts!
Anyone want a stab at the manufacturer?