Btw, this wasn't a correct statement of the issue.
"None has been found" does in fact mean that "none exists".
"Evidence" in science is like "evidence" in the law. Until it is discovered and recorded it doesn't exist. Indeed even the observation/discovery of the underlying factual material doesn't make it "evidence." It only becomes evidence when it's relevance to some scientific issue or problem has been elucidated.
Piling up facts is not science--science is facts-and-theories. Facts alone have limited use and lack meaning: a valid theory organizes them into far greater usefulness.
A powerful theory not only embraces old facts and new but also discloses unsuspected facts [Heinlein 1980:480-481].