But how would there be a CD from Wano if CDs all descend from founding kings?
A family that ruled a Kingdom, could decide to leave their Kingdom and became a Celestial Dragon
by doing so, they put another family on power and erased the history of the previous family leading that Kingdom
that's what happened to the Donquixote family in Dressrosa
same thing could've happened to the Venus Elder guy from Wano
maybe his family ruled over Old Wano, they left Wano and became Celestial Dragons, then the Kozuki took over and made sure to never join the World Governament after that
and they had Ryuma's help to scare them away from trying to force themselves into taking over Wano