We have always visited Japan with RT tickets from the US. This time we are using miles on JL for inbound and UA for return back. I have heard that this can be a problem. As I will not have the BPs for the UA flights I will have the ticket numbers and receipts. Is that sufficient for a check in agent for JL to confirm we have return tickets and let us board?

On another note, my husband may have a business trip from HND out of the Japan, a few days after we arrive. He will come back 2 days later to rejoin us. If the meeting is cancelled and he just stays in Japan the whole time with us will immigration officials ask about this? I am sure I am overthinking this.