You know, before this, the only one that I had noticed was the change in the yell when the Twilight Thorn flips the battlefield (since the yell was iconic) but I never noticed the other ones.

Good question! The Ventus Shift is how Jesse McCartney "infected" his future voice lines for Roxas with how he performed as Ventus. The vibe between the two characters is completely different, but McCartney's recordings for Roxas that were made after BBS frequently sound very close to Ventus. Also I don't know who I could be forgetting, Organization XIII always had Thirteen Members last I checked. (Maybe if enough people say something I could uh, remember). Listen to the difference in these two links.

https://www.youtube.com/watch?v=HUaDiIs9cpA

https://www.youtube.com/watch?v=QibsgmK00vg

In the first, you can clearly hear a deeper and generally more mature voice. The second voice sounds much less mature and, well, more like Ventus in BBS than Roxas.

I feel like you've forgotten someone, but for some reason I can't remember her name. Hmm :P. Also, what is the Ventus shift?