The term is a colloquial, grassroots label. It does not mean that the Internet Archive struck a deal with Cartoon Network. Rather, it refers to a specific set of user-uploaded collections that offer something the official streams do not:
Discovery, rescuing princesses, and Finn's growing attraction to Princess Bubblegum.
As streaming services continue to remove content for tax write-offs or licensing shifts, the Internet Archive has become the "Fort Knox" of animation history. The Season 1 collection there represents a time when Adventure Time was weird, experimental, and unburdened by its own massive mythology. How to Find It