first of all,its important to know that sometimes our artists who went to kora did not go if they did not know they'd win at least something, also apart from the kinshasa-based guys who found it suspect,there was also vieux lokua kanza if i remember well who was in the jury and also had some doubts,if i recall well another big african artist in the jury also said something
koffi was not meant at all to be in two categories and ended up being there at last minute
also, i often heard apart from the case of koffi that producers used to "pay" some koras to promote themselves
and to convince some artists they were granting artists they'd win koras if they signed for them