class s has always been code for lesbianism and was a taishō and shōwa era way to write lesbian fiction without state or social backlash.
tho, by the time yuri develops as a term for lesbians in gay magazines (as a counterpart to bara) in the late 70s and especially by the time it's taken up as a name for the genre in the late 90s, class s as a genre was already dead and it had been decades since class s social dynamics were a typical part of japanese culture.
yuri is mostly a heisei and reiwa term where class s was a taishō phenomenon and taishō and shōwa genre.
