I did some edits on GiTS SAC OST+, so I can easily explain my edits.
As written in notes, some artists are not credited, mostly Gabriela Robin as vocalist on all her tracks (3, 7 and 13). Origa vocal credits for track 18 are also missing.
Source for uncredited stuff are by logic not on release itself... but is there any sense to put lyricist for track 3 and 13 without a vocalist? And vocal for track 16 without a lyricist? No, of course. Not to me.
Track 7 is more touchy; there's only a "music: Yoko Kanno" in booklet but one can definitely hear singer starting at 2:02. So definitely not a music but a song.
At first, I found this cross interview:
http://www.kokaku-s.com/sac/backstag...002/index.html
You can see singers are all in brackets. That already confirmed singer for all these tracks.
Finally JASRAC gives credits for all of them, lyricist, composer, singer. Check by yourself.
So, in the light of this, I put credits followed by "[uncredited]" as staff told me.
We can do same here in notes; something like:
M3 vocal: gabriela robin [uncredited] words: gabriela robin
M7 vocal & words: gabriela robin [uncredited]
M13 vocal: gabriela robin [uncredited] words: gabriela robin
M16 vocal: ilaria graziano words: troy [uncredited]
About disc 4, M2, same check JASRAC if you want but only by ears you know it's Ilaria Graziano. Gabriela Robin has a quite different voice/tone. According to JASRAC again, Ilaria Graziano is the only one artist registered to have sung this song until today.