It’s not MP3, it’s Ogg vorbis
They’re encoding the top songs with higher resolution, the next bunch ( it’s still millions of songs) with about half that bitrate and not planning to save the next tranche which is like a looooot of songs but each has less than 1000 plays over the history of Spotify.
This is what I vaguely remember after reading the whole original post AND after a night drinking.
No nitpicking.
They never stopped selling xps, what drug is Tom using?