I do indeed see what you are saying about Corey being one of the four. The only problem I have, however, is with Shade telling us this before Lin's event occurring, then what was the point of him showing us Lin's event? Although he could revive Corey, as you said, and it would give a reason as to why he even took Corey's soul besides just cleaning up, I'm not sure how reviving Corey would benefit in anyway. But maybe having Corey around is needed to fulfill whatever shade has seen? I guess we'll find out about that soon!
Actually, I just thought of a possible answer to my own question.(This is assuming Corey and Kiki were the 2 souls taken, meaning Amaria and Lin should be safe at least according to Shade's message) As we have seen from the first 3 events, all of them have come true even if it didn't result in a death. So maybe Lin ends up exploding somehow and everyone believes it's finally over, but only the player character(through Shade's message), Shade and possibly Anna knows that Lin is not finished yet.
I recall Anna not being able to see Lin when she was attacking Saphira and the Giant Steelix, maybe the explanation for that comes into play for explaining how Lin would be able to survive that explosion, hence keeping true to Shade's message where only two souls are taken from the foreshadowed events.
Just throwing some ideas out there to maybe turn on a light bulb for some people.
This caught my interest, I'd also like to hear more of your thoughts on this.