The tail end of "Leaving This" was tried on Pale Haunt, I can't remember which song... Larry night remember.
We tried it, and the idea came up after I had recorded all my death vocals, so my voice was cashed, and I couldn't sing clean at that point after a LONG evening of growling. We did it with keys or guitars or something instead, and Dan Swano actually talked us into leaving it off the song. Larry then added the idea to "Leaving This" instead, and in my opinion, I'm glad it worked out that way, because they epic ending of that song is a highlight of the CD for me.
That, and Twilight Innocence might be the only two "left overs" we've used again, and like Larry said, Twilight was a left over really, it was just incomplete.
We usually have a few songs that don't make the cut after each CD. When we go back and listen to the songs later, we always realize the newer material we have is better. Writing this new CD, we've already discarded several ideas, and recently pulled a riff or two from the dead songs. It's all a process for us to give you the BEST possible songs we have.