Well Xenos, if it's a 3 year it's definitely out of date. As sean said, there wil be an identifying sticker on the bottle stating the new test date, if it was tested.
Try contacting H-pac on 01902 494988, they may be able to help you regarding the claimed test that was done. If you ask them about the 5 year test, they will tell you which bottle types are 5 year, or 3.