The missing song is "Nagashino (Oda)" , it should play at Battle of Nagashino Oda, but because of a bug, the song is missing in the PS3 and Vita versions, and plays "Itsukushima (Mori)" instead.
So yeah, this game is literally impossible to platinum in the PS3 and Vita, until Koei fixes this bug and put the song in the game.