Rereading Volume 5, I can't see how Captain Kuro's "disappearance" act ever got off the ground.
Okay, you brainwash someone to claim he is Kuro, and someone else to claim he's captured the first person. Still, when he goes to turn the fake-Kuro in, wouldn't someone look at the wanted poster, and immediately dismiss the fake? He looked nothing like the real Kuro except for the outfit.
I sort of wonder what happened to the "capturer" too.
If it were that easy, why wouldn't you see pirates all the time dredging out a corpse to give to a (not obviously related) associate, who then turns it in for the bounty on their head? It would be the perfect way to milk the World Government… claim a few million beri from them, stay low for a little while, then re-emerge, forcing them to reissue the bounty, repeat.