Authenticating a $2.5 Indian in jewelry piece

I've been reading about how there were some very good $2.5 fakes made in the early 1970s. I'm examining a $2.5 in a ring and it's definitely not an obvious fake. I don't think it's a counterfeit at all but was wondering if there really are fakes that are so good you couldn't tell?
It was XRF'd at dealer and was sent to a secondary authenticator but I don't know how much of an expert that authenticator really is. I've studied it very hard myself and while I can't weigh it, it does look right and have tested it with a Kee and Sigma wand and the composition shows as being correct. I don't see tool marks or obvious impressions or raised lines. But a lot of the edge is covered.

Does anyone know how good are the best fakes and was there any estimate on how many might be out there? I've read that the gold will be correct in many of the fakes as well so I still have some concern but I can't point to anything being off about it. No issues at the neck. No raised spikes. Just scratches and dents.