> You're right, there is no way to cryptographically prove that there are no contracts external to the blockchain.

But there is a very easy way to prove that there are not contracts external to the blockchain.

That's the whole point of an audit.

And it's very telling that they don't want their books audited, but repeatedly point to a clearly incomplete (from the perspective of someone who is concerned that the business might go under) as proof of solvency.