[ninthcat]

The probability is exactly zero by definition. The maximum score on a test is a raw score of 100%. Tests are normalized to have the reported scores fit a normal distribution. An out-of-distribution score indicates an error in normalizing the test.

In other words, the highest IQ of every living person has a defined upper bound that is dependent on the number of living people and it is definitionally impossible to exceed this value. Reports of higher values are mistakes or informal exaggerations, similar to a school saying a student is one that you would only encounter in a million years. By definition it is not possible to have evidence to support such a statement.