The only people on the rich list are the parvenus like Bill Gates and Jeff Bezos. The really rich seem to hide their money in various trusts, and avoid paying taxes on their wealth. I read a report by an ex-banker who estimated that almost half of the total wealth of the world is controlled by the City of London. Of course this is done through a variety of trusts in tax havens such as Jersey, The Cayman Islands and others. Property is hidden by using a hierarchy of holding companies and trusts ( a British invention ). There is even a name for it, it is called "The veil of Tiers".
The richest people in the world simply honestly earned their money and are not afraid to show them, as they all earned their personal mind and work.
The rest of the richest people in the world just do not want to show their real money hiding them in offshore accounts, because basically it is stolen money and it is 100%.
I'm sure many people's fortunes are greater than Warren Buffett's, but official sources can't confirm these finances because they're hidden and we have what we have.