My understanding is that an attestation that you have a billion dollars looks at your bank balance, and observes that you have a billion dollars in your accounts.

An audit looks at the history of your overall financials, to ensure that you didn't just borrow that billion dollars two days ago for the sole purpose of passing the audit. Or that you didn't, like, cash a half-billion dollar check from yourself to yourself, and have the money immediately show up in the destination account, before it was debited from the source account.