Thanks for the links Discofreak. The first didn't really supply any information other than what I read. And the second gave a clue but still lacked how it would be done in a full sound studio with proper multi-tracks.

I can't imagine cutting and splicing on tape like this to edit a mix together. I've done it to cassette when I needed to repair it. I also made my own remixes by recording from vinyl direct to tape and cutting it live. And with perfected timing it sounded quite good. But not too professional since I lacked multi tracks and loops like that always sound fake. As evidenced by fake remixes you can find on the internet.

Well I'll see if my thread invites more discussionn. This only touches the surface really. There are other factors involved like varying BPM of real songs and how these were marked and edited.