Measuring "accumulated wealth" can be really hard.
Or rather, not hard when counting the wealth of most of us, but really hard when counting the wealth of a person who can afford a pile of expensive accountants and lawyers to create a worldwide mesh of trusts and corporations - perhaps with some "mixers" where the wealth of multiple people is aggregated but who has what amounts is masked - with those mixers having their own sub-trees. (Basically I am describing trump org.)
I had to fill out some of the US Financial Crimes agency's Beneficial Ownership Information Report (BOIE) forms. I thought it was a good idea to help penetrate these corporate/trust webs. But El Cheeto cancelled that data gathering.