Trey's Notebook isn't a perfect measure of predictability. Since it completely disregards stuff played in the last 3 shows, it will consider Crowd Control on a gap of 4 more likely than a Moma Dance on a gap of 3. I think this is particularly important, since if a song was in a 3 show rotation, it would count as being a surprise song! But if it moved to a 4 show rotation, which a lot of songs are these days, it becomes OH so predictable. In a way, phish is being punished in your system by moving songs from a 3 show rotation to a 4 show rotation. If you can find a way to adjust for that you might see that line flatten right out.

Also those numbers are inflated from the number of songs in Trey's Notebook. Sure, it can predict 65% of songs played, but they list 36! The bigger that number, the more 'impressive' that percentage gets.