The Character Died with Him: Kaneto Shiozawa, the original voice actor for Zato-1, died from injuries sustained in a tragic accident. After that, Zato "died" and his body was taken over by Eddie and he has been voiced by Takehito Koyasu... until Xrd, when he suddenly went back to being Zato-1, and still with Koyasu as the voice actor.
So far, Baiken has three. The original one, used exclusively in The Missing Link was Satomi Koorogi (the voice of May), who previously was the voice of Sakura (but not Mayo Suzukaze, who voiced the actual Kenshin Himura, off whom Baiken was based). The second one is Sudo Miho, whose deep voice acting was used in a good portion of Guilty Gear games, at least up until Accent Core, which had Chizu Yonemoto instead.
Averted with Testament. His voice actor from X onward is Akira Kobayashi, who uses aliases every single game. So far there's been Konishi Kobayashi and Kobayashi Katsuragi.