I have to wonder if some of these unknown track were scrapped tracks from M64. I have a sinking suspicion the 3 Factory tracks were meant for Motos Factory (and the song would've presumably been dynamic like HMC's and JRB's music)
I remember hearing this sounds over and over from my neighbor. I was still a kid and he was a teen. It put me in a happy mood listening to the sound of Mario Kart 64