Actually, there are some other differences, but from what I'm seeing through searching google is that JCOA is either a Mexican costume jewelry manufacturer or some other identifier I'm not familiar with. Having a very difficult time finding clear and solid info about it through google.
Jcoa. And it was found in a location that has been under water for 50 years,I'm not saying It couldn't have washed out there, or fell off of a finger pulling in a fish, but! I find old stuff there all the time.