Originally Posted by
AutoSlash
I know OP's concern is likely long past — but replying since this post pops up in search results.
JL isn't a B6 partner for any mileage earning, but they still have a codeshare agreement covering flights out of JFK and BOS. Seems to be one direction only — JL codes on B6 flights, rather than the reverse.
ETA: no idea if this will work on separate tickets — but it's possible to book B6 and JL flights together on a single AA award. AA's move to dynamic awards has made combining AA flights with partner flights quite annoying, so I suspect it's something we'll see more often.