That quote was supposed to mean there could be one more track besides 1-03, 1-05, 1-06 and 1-12 that was originally composed by Masaharu Iwata,
because Iwata composed five tracks in total on the original Mushihimesama. Maybe you could rewrite it. I think what I tried to do can be achieved better by providing the composer credits as below;
1-01 Composed by Manabu Namiki, Masaharu Iwata
1-02 Composed by Manabu Namiki, Masaharu Iwata
1-03 Composed by Masaharu Iwata
1-04 Composed by Manabu Namiki, Masaharu Iwata
1-05 Composed by Masaharu Iwata
1-06 Composed by Masaharu Iwata
1-07 Composed by Manabu Namiki, Masaharu Iwata
1-08 Composed by Manabu Namiki, Masaharu Iwata
1-09 Composed by Manabu Namiki, Masaharu Iwata
1-10 Composed by Manabu Namiki, Masaharu Iwata
1-11 Composed by Manabu Namiki, Masaharu Iwata
1-12 Composed by Masaharu Iwata
I know this looks messy, but it at least prevents someone from having a wrong notion that the rest was totally composed by Namiki.