I broke a BOS-SYD, SYD-LAX ticket and was issued a AA codeshare JL metal for BOS-NRT on JL7/AA7375 and a JL 771 for NRT-SYD, and AA 73 for SYD-LAX. I used the JAL site and JL record locator and could only see my JL flight to choose seat. At 72 hr, I could check in the JL flight, I decided to call JL. The phone rep told me to go through AA and I replied that I had already done that on AA and I could only see the AA flight when I check. however, she told me to use the check in button at the top left of the screen, and lo and behold, when I clicked on it,I got moved to the same JL checkin site, but this time, the JL7 flight appeared as well and I was able to checkin and issue the boarding pass. I thought I knew but this is great.