LITTLE KNOWN FACTS ABOUT WHAT IS THE GREATEST SONG EVER WRITTEN.

There are 7 meanings stated in OED's entry for your term greatest, one among which is labelled obsolete. See ‘This means & use’ for definitions, usage, and quotation proof.It was the longest solitary—in runtime—to get to the prime British charts at that time, and in 2013, Billboard journal named it the tenth most important song of all time