On the back of Marvin’s where the songs are listed, why does it show different band members names next to the song titles?

For the record, this method of annotation appears on all track listings for every album.

Contrary to UNpopular belief, the name(s) next to each song indicate who wrote the song.  Up to this point, the way the band typically works is that each songwriter works on their songs individually and then once they’re fairly near completion, they take the songs to the group to iron it all out.

So, he who wrote the lyrics is the same person who wrote the music.  Consequently, this also usually results in the same person being the lead singer of the song.