Google turns up some years-old threads but there seems to be some contradictions and loose ends.

Connecting from a UA inbound flight to a JEJUAir (7C, though it was ticketed with a H1 flight number) at ICN (international in, international out), then the reverse on the way home. All flights are in the same PNR, displayed on UA.com and it was an itinerary offered by ua.com when I was looking at options but it appears the client's TA ticketed them separately (UA segments show a 0167... ticket number, H1 segments show a 1697... ticket number. It looks like JEJU positions itself as a LCC. UA transoceanic segments are in J (via PlusPoints)

• Is UA able to interline bags / will they be able to through-check it or will I need to claim and recheck in ICN? [I've had success with UA automatically through-checking bags on single PNR/different ticket# itineraries with OM and 4Z but JEJU seems...different...than those]
  • If the latter, how anyone have experience with the "how" and "where" of that at ICN?
• Same question for boarding passes?
• For the return, any guesses as to what baggage allowance will apply (JEJU's 15Kg, UA's 50# Y, UA's 70# J)?
• Through-checked or claimed and rechecked at ICN?
• Will JEJU be able to issue boarding passes for the UA segments?

(mostly worried about the baggage as 15Kg is borderline for where my bag usually weighs in and the excess weight charges seem rather excessive...or maybe my expectations about bag fees are just out of whack)

Thanks in advance! (And if no one knows I'll update here during/after the trip for the benefit of future audiences)