Errors in writing, voluntary changes by the bearers, modifications for language reasons... There are many reasons why the surname Jjoo may have undergone changes or modifications, and from those modifications, surnames similar to Jjoo may have appeared, as we can see.
Discerning whether the surname Jjoo or any of the surnames similar to Jjoo came first is not always easy. There are many reasons that could have led to the surname Jjoo being written or pronounced differently, giving rise to a new, different surname Jjoo with a common root.