The other thing to note would be the number of addresses that have a balance but have not been touched for years. Of the many reasons included could be that passwords or keys have been lost/forgotten.
that's the problem with these estimates, they are purely guesswork.
there is an equal chance (if not higher) that the early adopters who own these funds are still holding it and more. for instance someone from 2009 can have one address with 1000
BTC in it as his cold wallet and a hot wallet with 1-10
BTC in it using THAT for his hot wallet spending,trading,...
for instance i started with bitcoin in 2014 and i have funds in an address from that time that i have not touched yet and won't touch it for another 10 years probably. so far it is about 4 years of them not being touched, that doesn't make them "lost".