the OP will find a must inspec date stamped into the tank, after that no propane supplier will legally be able to fill it....

I dont know how they inspect such large tanks, it might be like high pressure gas lines are inspected at weld joints. they are X ray.......

but the method doesnt matter.

try calling a totally different gas supplier perhaps at the other end of your state to get answers....

and be sure to ask about large propane tank inspections