I wasn't saying they vet claims per se; I was saying they almost certainly have to vet people who sign up for Content ID in the first place. Which might explain why they limit signup privileges to known commodities. (Or at least might partially explain it).
YouTube has business and licensing agreements in place with some of these content owners. There is absolutely no way they aren't vetting signups for Content ID in at least some capacity. For one thing, how would they pay people their rev share for premium content clips if they didn't have reasonable assurance those people really were MTV, or NBC, or Sony Music, or what have you?
Now, is my overall explanation overly charitable? Entirely possible. I really have no idea what goes on with this process. All I'm doing is offering a possible explanation.