The Kennedy had to be retired out of sequence. The Kennedy had originally been set to replace the Kitty Hawk in Japan, with the Kennedy scheduled to be retired in 2018.
The Kitty Hawk is due to be replaced by the Bush when it comes on line, but the Navy will remain one carrier short.
Last I heard G. Washington will replace KH in Yokosuka next year. There is talk of keeping KH in commission until Bush comes online just to keep the CV numbers up.