[pseudohadamard]

Uhh... mathematics and logic? Since there's no perfect UB detector, one that detects UB in 40% of programs can only be presenting a lower bound. And I don't know why you think C programs rely on UB, they have it present without the programmer knowing about it.

[uecker]

It follows from mathematics and logic that "larger than 40%" could be 100%, but it does not follow that this is likely or reasonable to assume.