I know, right? They have the individual version, so I thought they actually sing the song completely.
However, I noticed that in the solo versions, the voice is... "different". Some parts are recognizably from the original. The rest, however, seems like it was put in afterwards
It's kind of hard to explain, bear with me for a minute here.
It looks like that they actually opted for option 2: each seiyuu doesn't really sing the song completely, only pieces of it, to create an actual group song. However, as the song looked promising they called the seiyuus again to create a solo. Only, they're asked to sing only the parts that they haven't sung in the original, so the piece is complete.
I can feel that at some parts it is exactly like the original group song, while the rest is like something new: the intonation, pitch, and feeling is different.
I, for one, don't believe that they're only good at certain parts and that the difference is inevitable