Technically, all the deaths we know of have been suicide, but not all have succeeded.
1. Corey jumps off Beryl Bridge and dies. It's a suicide, so Shade appears.
2. Kiki, who knows she is going to die, does her best to stop Team Meteor, and goes out protecting Reborn. It's not really a suicide, so no Shade
3. Amaria can handle the fact that Titania doesn't really love her, and tries to kill herself by jumping off the waterfall (Crystalline Cascade?). She lives, so Shade doesn't appear. He still appears to tell you that only two deaths will happen.
4. We have no idea who this is, though there are possibilities, so this person might live/die depending on if Corey's death counts.
Then there's this deal with the fifth screen in the power plant, so everything is just speculation until it shows up in game.
Also, the 4 deaths could mean the original holders of the 4 keys.