Gah.
Holy you people don't understand anything about the stamps.
The stamp is a government certification that the bottle the stamp is on is approved for holding a compressed gas. This has nothing to do with millenium - either it's legal for the bottle to be filled with compressed gas, or it ain't.
Getting the stamp has *NOTHING* to do with testing. Whether or not a bottle has a stamp is determined by its design - if it's manufactured to an approved specification, it gets the stamp, if not, then not. The only thing TESTING does is extend the EXPIRATION DATE.
Now, what you MAY want to look into, as I have no idea if this happened in Europe or not, i whether your particular model of bottle got approved for whatever standard it is that gets yu a pi mark AFTER the date of manufacture for your particular bottle - you'd probably find that out at your bottle manufacturer's website.
But, again, this has *NOTHING* to do with millenium and everything to do with the laws your governmetn has created regulating compressed air cylinders.