Netflix uses the same algorithm and suggest you titles that will never touch the platform...
If the point 3 it's true, someone create a free account on freshtunes or any free platform like that and upload Perhaps. If the track is preloaded for leak prevention, well, the system will takedown automatically (the takedown happens in the upload process, they don't upload songs with copyright lock) and will never appear on spotify. If the track appears on spotify (even for just a few minutes), it's a myth.
Even if the track was reworked, we all know the vocal track will be the same, and the content id will identify automatically.