There is a difference between Nightcore Mix and Sped Up.
"Nightcore Mix" is a term which describes the style of speeding up Eurodance, Techno, Hands Up, Dance and Trance music.
Music which doesn't classify as "Nightcore Mix" but as "Sped Up." are the other kind of genres, like Pop/Rock music which uses the same technique of the Nightcore music.
Since this kind of music remixing was born as Nightcore and not as Sped Up. then it would make more sense to rename everything as Nightcore Mix in this case then.
"Nightcore Mix" is a term which describes the style of speeding up Eurodance, Techno, Hands Up, Dance and Trance music.
Music which doesn't classify as "Nightcore Mix" but as "Sped Up." are the other kind of genres, like Pop/Rock music which uses the same technique of the Nightcore music.
Since this kind of music remixing was born as Nightcore and not as Sped Up. then it would make more sense to rename everything as Nightcore Mix in this case then.