Evolution in the Percentile's regarding fossil evidence

Listening to a Debate tonight I heard an evolutionist say "we have fossils of 92% of all forms of life that has ever lived on earth"

Now how do we know we have this much?
To say this the person stating it or the article and scientist stating the original statistic would have to have supernatural knowledge of life before man's History. They'd have to know the creatures that didn't die in the condition to petrify. For all we know that 92% is really only 40% of all the life forms, species that ever lived.

Saying this number is averaged out of what creatures we have examples of today. if there were many animals over a period of 1.3Billion years that we never could conceive of or haven't pieced together to get a full picture of with their bones as of yet only shows that we have an unknown roof of life-groups since the history of life on earth.

saying any %percent of animal remains is known implies we know that there's a number discovered out of 100% and are missing 8% of them. This is a HUGE problem for the true optimistic scientist and shows they really have wishful thinking about their own studies.
Sure we can say that there are methods of measuring how many fossils are in a quadrant of a mile and go according to how many miles have been explored by palaeontologists. This is still a vague measurement and unstable method of getting a valid number of fossils. We could say it's estimated but these evolutionists don't say that, they boast the number as though its fact and I'll keep wondering who it that has the missing 8% is. what's the projected time in which we'll discover the remaining 8 if it's not simply missing. BTW logic dictates that you don't know something's missing unless you know it from the whole.