Far enough to document lawful acquisition and the route of the actual invested capital. A current balance alone may not answer either question.
Follow the money to its origin
Start with the event that created the capital: salary accumulation, dividend, business sale, property disposition, inheritance, loan, or gift. Gather the documents that establish ownership, value, tax treatment where relevant, receipt of proceeds, and deposit into a named account. Then follow every material transfer to the new commercial enterprise through statements, wire records, escrow records, and subscription evidence.
If funds are pooled across accounts or currencies, prepare a dated reconciliation that explains the connection rather than relying on a broad assertion that the investor had enough wealth. Gifts and loans may require records about the donor or lender as well as the recipient. A cash transaction, late-added document, or inconsistent address should be addressed honestly, with corroboration where available.
Translate foreign-language records completely where the process requires it and retain the originals. The objective is not to submit every document ever created; it is to make the lawful story of the particular investment understandable from primary evidence. Good organisation early can prevent an avoidable gap when later transfers or project records need to be checked.
Source records should be indexed by transaction, not merely piled into categories such as ‘bank’ or ‘tax.’ A reader should be able to move from an invested dollar backward through each account to the lawful event that generated it. That organisation also helps reveal a missing statement before the filing is prepared.