The many John Carters of Anime.

John Carter is the name of a 2012 film adapted from a 1912 Pulp Sci-Fi series originally titled A Princess of Mars but it and it's sequels are often called the Barsoom series. 

The way this movie was seen as so generic despite how it's source material predate everything it was seen as derivative of has made it a euphemism in my mind for all similar scenarios, something highly influence that later fell into obscurity and become overshadowed by it's children which got high profile mainstream adaptations way sooner.

For Otaku Media the comparable situations are mainly source material from the 90s or early 00s that didn't get a full TV Anime adaption till the 2010s or 2020s. 

The big one I've already talked about is YU-NO: A Girl Who Chants Love At The Bound of This World. It's 2019 Anime was dismissed by casuals as just another Isekai but with a drawn out Steins;Gate/Re:Zero set up thrown in.  There were not zero Isekai prior to the 1996 release of the YU-NO game, but it still long predates the main formative texts of modern Seinen LN Isekai. 

But those kinds of Anime aren't the only ones I feel YU-NO influenced in some way. When I was watching it not even knowing how old the source material was yet the talk about being "outside the four great Ancient Civilizations" reminded me of exposition from Madlax a not largely forgotten 2004 Anime. Mio Shimazu I feel is a very formative early Tsundere and Kanna Hatano likewise is an early formative Kuudere. 

John Carter the film you can argue doesn't do itself any favors in avoiding the Generic accusations in how it presented itself.  And YU-NO it similar, as much I love the 2019 Anime I do lament that it's using the modern character design revamps of the game's then recent remake. In 2026 we have Anime like Red River showing us a modern Anime can still feel faithful to it's original 90s Character Designs. 

Red River can indeed be added to this list, as a classic Shoujo Time Isekai it's Manga predates Inyuasha. 

But another big Visual Novel example is Muv-Luv.  It's original release was 2003 and the first version adding Alternative to the title was 2006. There was no proper adaptations of a version of it's main story till 2021-2022, but it has spin off Anime in 2021 and 2016. 

The pilot of the 2021 Anime is one that I'm sure watching no knowing the history of Muv-Luv would have been comparing to the pilot of Attack on Titan, but it's Manga didn't start till 2009. It all shares a lot of vibes with many modern Gacha game based Anime. 

There are of course some major important early Visual Novels that still have no TV Anime. Shizuka, Kizuato, Silver, Cross Channel, Tsui no Sora.