Insurance companies have a sheet that tells them what the safety standards are. most glaziers are required to have this information too. if you are to be covered by insurance on a tank, most companies would require the tank to meet the standards prescribed (thickness and type of glass). the standards are a bit over the top according to me, but it safe guards the person buying the tank, the person selling the tank and the insurance company in the event of a claim.
most tanks are not made to insurance or the glass association's standards, but are still safe. its a gamble. I have comprehensive house insurance with vero, and i know that my tank is covered. maybe ill call them up again and make sure.