I don't doubt that one bit
but if it's one thing I've learned it's that there will always been an opportunity for things to get missed or crossed in communication.
On the one hand the public does expect insurance agents to look out for them and the good ones will (and I imagine you've had a good one so far) but on the other hand the public is also really responsible too on their end.
I'm more just more speaking to the viewpoint of it's not covered it should be on the agent then since you asked. That's a gut reaction many of us would probably have and sometimes it really does lie with the agent but the majority of the time..eh...unfortunately no.
As far as your ring generally policies are written where if the jewelry item is below a specified $ threshold it's covered (generally speaking here) without being actually specified the exact item but if over a threshold it needs to be scheduled (that's basically saying adding a rider) onto the policy. The value often determines whether an appraisal is needed. I'm glad you have that covered