Technically this study defined “lost” as commercially unavailable, meaning those 87% of games can’t be bought legally, but they’re not lost forever. We have entire console libraries from the 1970’s to the 2000’s available online. Old PC games I’m not so sure about.
Technically for a game to be “lost forever”, it would have no physical cartridge, and nobody ever found a way to dump it onto one. Which is extremely rare and borderline impossible for games before 2010.