Slag, the way I've heard people sing it is, "and the joy we share as we tarry there, none other has ever known".

You could interpret it this way: Every person experiences his or her own joy in a totally unique and personal way. Therefore, no one can ever know exactly what that is like for any person other than themselves. Everybody's experience of it stands alone.

It doesn't imply to me that no one else can HAVE the same experience...just that their perception of it would be unique.