With a continuous evidentiary chain rather than a summary: the records showing how the asset was lawfully acquired, the sale documents and valuations, tax filings across the relevant years, any loan and its discharge, and bank statements tracing every transfer from sale to enterprise without unexplained gaps.
Build the chain forward, then read it as a stranger would
The exercise has two halves that are easy to conflate. Demonstrating lawful acquisition of the asset can reach back years and rests largely on tax records and title documents. Demonstrating the path of funds is a banking exercise and fails on small things: a transfer through a relative's account made for convenience, a currency conversion at a private dealer, proceeds split across institutions and partly spent before being reassembled.
Every hop needs a statement showing the amount leaving and the same amount arriving. Hypothetical example: a family funding an investment from timber rights sold off a woodlot in three tranches over four years finds that the second tranche was paid to an adult son who then bought equipment for the farm, and the amount now in the investment account no longer reconciles to anything a reviewer can follow. Reconciling a chain like that after the event is possible and expensive, and it is far cheaper to keep each tranche in its own account from the day it arrives.