Actually, I don't quite see the point of two separate "lesbian" genres at all.
Shoujo-ai is supposedly the base genre for lesbian romance, subtext, and annoyingly often even just for side characters with (minor) lesbian tendencies.
Yuri is shoujo-ai topped with the occasional nudity and sex scenes.
Smut is the middelground between conservative/pure romance and full blown hentai.
Hentai is pure sex (18+ manga)
Ecchi for fanservice
... Why not simply combine smut and shoujo-ai instead of using yuri... Or simply get rid of shoujo-ai and replace it with Yuri altogether... Now MU kind of insinuates that Yuri means lesbian sex (which it does not).
And we now have to contend with 4 separate genres to indicate homosexual manga... Where 2 would suffice (and be better in my opinion), when having already indicated a manga deals with lesbian pairings, isn't a simple tag called "smut" enough?. I most certainly won't be confused by it... If you'd like to indicated a manga contains lesbian+gay pairing and gay sex only, that would be something for the "tags" (or categories), NOT genres.
So to respond at the topic title. YES, it's definitely Yuri. All manga containing Lesbian (romance) are.
Shoujo-ai is often the incorrect term, since it insinuates that it's love between (young) girls... Which kind of makes it also lolicon?
Anyway, /rant
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