> In a sense, I already do disclose such data in a general way, because whenever I write or say anything about startups, I wouldn't contradict trends I know about.
That's a bit circular, if people would question the things you write or say about startups, you'd tell them they are backed by empirical data, then when someone asks for this data you tell them its implied by the things you write or say about startups.
I can totally understand why most of that data is hard or impossible to disclose, that's obvious. But you can't cite secrets as evidence, all you can do is say "trust me, I know what I'm talking about". You can't have your cake and eat it too.
Obviously no one is questioning the existence of that data, nobody's suggesting you're cooking it up, they're just wondering if they'd spot the same patterns in it as the ones you perceived to be there.
To sum it up, whenever you write or say anything about startups, the only thing you disclose about such data in a general way, is the conclusions that you drew from it, what you perceived (not "know") to be a trend, which is probably useful and very valuable, but is something entirely different than the data itself.