No laboratory test can ever definitively guarantee the 100% absence of any compound. All equipment, all tests, all procedures have limits of accuracy. A definition of what is meant by a phrase 'does not contain any x' is always required that takes into account the technological limits of the tests employed. It might mean 'below 5 parts per million' or 'below 2 parts per trillion' or whatever, but it can never be '100% absolutely zero'.
Australian law requires that wine containing added sulfites MUST be so labeled (preservative 220). Many other countries do not have this rule. I don't believe France does, for example. This means that unless a bottle is Australian (or you know of a similar rule in the country of origin), in the absence of information to the contrary, you must assume that it does contain added sulfites. For the simple reason that almost all wines from all countries do.
This brings up another point. While it is true that almost all wines contain added sulfites, I think WineIntro.com's assertion that wines without added sulfites are extremely short term propositions is very simplistic and in many cases simply wrong. My experience, and I believe the experience of dozens of wine makers in Australia is that this is just not true.
Two examples that I have personal experience with are Jasper Hill Emily's Paddock Shiraz / Cabernet Franc, easily one of the top 5 wines from Australia, and its sister Georgia's Paddock Shiraz which is certainly in the top 25 wines from Australia. I have purchased a case or so of these wines every year for over 20 years.
Jasper Hill is not only a strong advocate of bio-dynamics but as far as I can tell none of their wines contain added sulfites. They do not bear the Australian preservative 220 notice and this means they would be operating illegally if they did. Now I don't claim to know how Ron Laughton at Jasper Hill avoids the spoilage for which other wine makers add sulfites. But I do know that I am currently working my way through my 1997 Emily's, and I assure you they are in magnificent shape and drinking beautifully after 12 years.