In the past there have been a few programs admitting that tracking is not and cannot ever be perfect.
Gooner’s one percent sounds above average to me – maybe sports places do better, or Gooner successfully eliminated programs with less accuracy.
My own estimate is 10 to 15% lost, and this is just based on talks with industry people.
In addition to Gooner’s explanation, there are also players who will delete the “tail” on any URL when possible, thinking it must be something sinister.
Also, look at the bottom pof your browser. IE has a little “eye” there, which appears with a “blocked” sign. You can click on it and see which cookies have been blocked on that page. This happens even with medium security settings to third party cookies. Don’t know about other browsers, but the majority of surfers does use IE.