On that list, some million sellers from the late 1970s/ early 1980s are missing ("Rivers Of Babylon", "Das Lied der Schlümpfe", "Sun Of Jamaica" and "Words"). All these singles were certified platinum which was one million singles at that time. However, platinum was already lowered to sales of 500k in 1987 (and not in 1989), so "Lambada" has a sales total of one and not two million. "The Ketchup Song" is another million seller that is missing on that list.
All the singles from the 1990s are listed correctly according to their certifications. One single that was never certified is "Das Boot" by U96, I'm sure that it sold at least half a million copies, maybe even one million (it was 13 weeks at number one in 1992).