The example you give cannot happen or should not because the market capital only relates to floated stock. If Bill Gates owns 10% of the company and its the same stock he held since the 1980's then its not part of the market cap. Same should apply to Bitcoin really, if the address is never used then its not part of the fairly rapid monetary velocity which makes up Bitcoin value. That guy who lost his laptop in a landfill doesnt count as value, theres HODL and theres lost to any practical use forever so clearly he and that address should not be popping up on TV screens as 'the value of:'
As it relates to equity market cap, traditional market cap is simply outstanding shares x market price... what you are referring to is float-adjusted market cap. Generally speaking, indexes are float-adjusted, example, the S&P 500, whereas individual company market caps aren't. This obviously depends on the data provider but in most cases you are simply seeing OS x MP.