Probably a misinterpretation of “not offered for sale today”.

No, that is "archived in any known library". Source is the Video Game History Foundation.

https://gamehistory.org/87percent/

https://insider-gaming.com/study-classic-games-unavailable/

No. That study states "...whether they have been reissued or are otherwise still available through their rightsholders.". Takem from the first page of the PDF.