“The real numbers are something we cannot know, because the overwhelming majority went unreported”
I think it would be better stated if you said: “The real numbers are something we cannot know.”
The part where you say “the overwhelming majority went unreported” is unprovable.
Is it possible there were more abuses than we know of?
Yes, possible.
However, it is speculation not fact to say “the overwhelming majority went unreported” because. . .well. . .it is unreported and we have no facts to say how many were unreported.
You can say you think such a thing but you can’t argue that as a fact.
IMHO.
You are correct. I cannot state it as a fact.