If someone started adding all the coins claimed to belong to someone (Satoshi, Winklevoss twins, Mircea Popescu, Bulgarian governments and so on), they'd quickly find that Bitcoin's supply is more than 21 million 
No they wouldn't. That's not how this stuff works.
No, but this is how the news work, fake or not, doesn't even matter, since all exaggerate.
Some of those numbers are for real, but not all. And if you start adding up all those alleged lost coins in huge amounts from the news you have a good chance to already get to more than the current supply.
agree, there is a statement - blockchain transparency is amazing, and we should use that one, when seeing news like this one
you claim that you have xyz BTC, just sign a message with wallets, that add to the mentioned sum, otherwise, you cannot be trusted, easy and working
nevertheless, I did not know the guy, was not even aware that he was part of the early community, read some articles today, but sad that he passed away, RIP