I'm having a hard time getting flights with JTA segments to show up on JL's websites. I guess I know the short answer to the why - JL and NU are different airlines and I can't expect them to be treated equivalently under all fare rules. But I'm trying to book a few trips with some JTA (Japan Transocean Air) segments and I'm running into some issues:

1) I'm trying to book OKA-GMP/ICN and JL's website will only return connections via NRT or HND. I presume that this is because connection via KIX requires travel on NU. The fare rules (on JL's website) are silent on valid domestic connections.

In the past I've booked OKA-BKK and the rules for that fare explicitly allowed domestic segments on JL or NU - and sure enough, connections via KIX showed up in my searches.

2) I occasionally search for JL tickets on JL's American Region website as it has a more sophisticated multi-city booking tool and often returns more flight combinations than the Japan site. However, it appears that NU flights never appear in search results. Try searching OSA-OKA - aside from the once daily (JL) ITM-OKA, every other result forces a connection through HND. JL and NU flights are presented together on the JL Japan site.

I'm trying not to get too hung up on the why - like why JL (apparently) doesn't codeshare on the NU flights, or why some fares explicitly allow an NU domestic connection and some don't.

If I want to connect in KIX, do I have any recourse besides purchasing 2 separate tickets?