I added a few more composer credits based on information from this album:
https://vgmdb.net/album/6228
I'm still not sure about M12, 18, and 19. Though M12 is from the game Mizuiro, which the album linked above says was composed by Riverside Music, Ebi, and Nakachan. However, this page for the Mizuiro Soundtrack...
https://vgmdb.net/album/2456
...says that the music is by Noriyasu Agematsu and Takehiro Kawabe, so I think something is incorrect somewhere.