Identifies the original exchange of the Bitcoin address in my ledger.
It is possible to trace backwards. Some blockchain explorers annotate exchange names (and other items) in addresses and detected wallets. Such information is only a clue and not evidence.
The required document is a receipt.
I don’t know that CSV archive exchange can be considered a receipt. There’s a chance that your revenue service will accept it, but there’s a chance that they won’t.
I would like to suggest you:
Get CSV archives from the exchanges you process.
Check for yourself whether your revenue service allows CSV delivery or requires a formal receipt.
Receive an official receipt from the exchange you traded with.
In general, we (currently) try not to sell large amounts of Bitcoin without first engaging appropriate legal counsel.
Never make large payments for goods and services with Bitcoin. That is recklessly opening the door to profitable services.
