If somebody remembers the song, especially but not exclusively after they forget who sang it first, it's part of "folk memory" and probably qualifies to be at least "potential folk."

If two people remember a song, especially after the original singer isn't around, it is almost a fact that they will sing it differently, hence it will already have been subject to what some call "the folk process" (but the composers just call "song mangling") and certainly has begun the process of "becoming folk."

The claim that "it can't be folk because it's pop" doesn't hold up against the fact that more than one of the current "originators" of songs/tunes now considered hard-core folk were, when alive, conductors of or players in their city symphonies and based many of their tunes on plagiarizations of (how revoltin') "classical" composers. (The classical composers retaliated by using "folk tunes" for their themes in some compositions, tit-for-tat.)

The valid question is only "is it folk yet?

John