Any previously posted content, whether posted in a previous contest or not, is inadmissable to the PrC Contest.
Furthermore, several times it has occurred that a PrC was posted first in the then-current contest and then outside of it before the voting was over (or before the thread had even been created). As I recall, while the Base Class Challenge at one time allowed this (though it has been retracted since), the PrC Contest does
not.
I do feel sad for NeoSeraphi for making the
Slowknife and not being able to post it in this contest, but I'm sure it'll be a great inspiration (or hey, maybe I should poke him, see if he still has some ideas left over that he could enter).