Probably prototype/unused tracks
Or even image songs like in
this release
.hack//ZERO Vol.1 ファントム・ペイン is the title for one of the .hack fiction.
And
this one, I have never heard the 5 vocal songs in the game, but well I never completed the third episode of G.U.
By the way
here is the last one
According some info I gathered, the disc contains arrangement with Tomoyo Mitani as chorus
and the tracklist
Didn't add it to database because I would like to do that after getting it, still no chance though.