I also asked on #StackerNews and got into a new rabbit hole 

https://stacker.news/items/583764/r/alashazam

there are 'burned coins' and lost wallets but the lost bitcoins are mostly the first category (the second type are still valid and we may assume that someday someone will access the lost wallet)

Hope it make sense

(I am still very new to that stuff, and get easily confused)