The one I bought through tiki torches was brand new but plastic on it molded in says manufactured 01/06 and the hydrostatic test says 04/13, although this was hand written on a sticker then sprayed with a clear coat. The tank may have been sitting around for years but definitely not used.
Had no issues with it so far other than the guy at uhaul filling it was complaining about some issue with the valve. He thought the connection was gassing a bit more than it should.
Had some strange issues with my woodland stove regulator seems like it sometimes (1:10 starts?) would run a weak yellow flame until I closed both the reg and the valve, then opened the valve and the the regulator and then everything worked fine. I think this may be from starving the reg off by closing the valve first at shutoff.
Hey, if you want me to take a dump in a box and mark it "guaranteed", I will. I got spare time.