I'm going to assume "classic" means "old stories that are legendary".
There are several classic authors that have multiple beloved stories from way back, including me considering my oldest story posted online was More and More back in like 2006 or something like that (under the throwaway alias Candy16). I have an archive link in my signature which stores most of my works from before the dreambook boards went down a couple years ago. More and More in particular has a sort of legend status to it because I have seen it reposted countless times on other websites, including being one of the very few ENF stories to ever be featured on ENF-CMNF.com. I also have a bunch or newer stories posted to this forum since I've been lucky enough to be much more active lately than I used to be.
One of the true classic legends was
TheSparkZone who was pioneering ENF stories way back in 2001 before they even had a name for the genre. Many older authors were inspired and influenced by her, including me.
While I don't have the time to hunt more links right now, other classic greats include:
Hooked6 and his massive library (half of which I can't even find anymore) with beloved stories galore, still going to this day.
SDS and all of his many stories, most famously the never-completed classic I'm Not a Little Girl, also still going.
Johnathan and the top tier Greenview Stripping Wars saga and the famous Pushed Out story (and other good ones if you can find them)
Splotch and the Kathrine series, which for years was the premier tiny-tit-ageplay-bullying saga.
The Erica stories, which if I remember correctly had multiple authors. They're in this site's archive.
Ribeye98's Thornwood series is top tier legendary for a swim team girl constantly being naked in school. It's very long.
Drew and Janie were extremely active classic authors back in the day with loads of shorter stories.
CaughtofLore had a handful of massively popular stories that were never finished, especially Compromising Positions which was so popular at its height that the number of comments in the thread broke that website's formatting all to hell, requiring him to make a second thread.
Ewong was a huge author with multiple shorter stories back in the ASN days.
Jappio has a huge library, most famously the Mary's Naked Adventure series
MFSBDB gave us the legendary Sibling Rivalry story
Gillian's Cops and Robbers story was very famous in the mid 2000s.
And a couple of 20ish-year-old stories that were highly influential in the early days were Karen Wagner's Naked in School and Becky Romero's public spanking sagas.
There were also several classic ENM stories, such as Tommy's Debasement from Blondie and Shelly the Sports Reporter from CaptQuixote. Swimkid was another legend who had a ton of stories of pitiful tiny protagonists, mostly ENM.
For all of the stories I mentioned, most of them are located either in this site's archive, the beachclub archive in my signature, Asstr and its various databases, or Blondie's Stripping and Humiliation boards.