This information is available to the public about the USD supply as well: https://fred.stlouisfed.org/categories/24
> The information on how much banks are holding onto in fractional reserves should therefore be available and make cooking the books more difficult and allowing audits to be more accurate and hopefully regulations could exist to keep banks better in check.
You should look into just how much regulation there is in banking, and the history of banking itself. All publicly traded banks are audited yearly, and yes I am aware of Enron/Arthur Andersen and the GFC of 07/08, among others.
No system is infallible, but investors trust US audited company statements 100x more than chinese audited companies, for instance.
If trading is done off-chain, or transactions are made between currencies, those are not a part of the blockchain. For bitcoin-only transactions between wallets, no exchange is required.