Seems like a nearly impossible number to prove. I would assume they are only counting cases where the accusations can be shown to be false (which will always be a much smaller number than the ones where the truth is simply unknown) and cases where the accuser recants (which will also be a smaller number and will include some women who had been telling the truth). It seems no more valid than the opposite extreme of assuming all accusations are false unless you can prove them true.

But what’s the alternative? Forcing every case into true or false no matter how little information you have to go on? Looking only at cases with overwhelming evidence one way or the other and pretending the rest don’t exist?

And that’s without getting into questions about things like unreported cases, or cases where part of the story checks out and part of it doesn’t. Are we only looking at formal complaints or are we including accusations that are only spread socially?

The whole question is vague and surrounded by assumptions. It’s like asking if aliens are real. The likely answer is going to depend heavily on whether you interpret that to mean “does any form of life exist elsewhere in the universe” as opposed to “are little grey guys practicing proctology on us?”