What's the deal with Kagain's multiple dialogues?

He's got KAGAIN.DLG, KAGAIJ.DLG, KAGAIP.DLG and KAGAIZ.dlg (with just one state). Now, I thought that everything but the first one are some special-case one-time dialogue files run from StartDialogue instead of Dialogue, or perhaps the NoSet versions. But, it seems, his dialogue does get set, because the Kagain in my current party, when looked at in the editor, has the KAGAIJ.DLG. This may explain why the EXTERN command I've put out to ~KAGAIN~ from another NPC's conversation fails, but what can I do about this? Sure, I can update all of his dialogues with the custom extra states, but I still have to put a specific dialogue file in those tildas for the EXTERN, and I have no way of knowing which one players' current Kagain will have.