Adding my recent award seat selection experience to the thread:

I booked two JAL J award tickets several months ago for myself as an AA EP and my non-status daughter for travel this summer. Somehow I neglected to get seat assignments immediately after booking so I called AA earlier this week and luckily we were assigned 7H and 7K on a 773. Out of curiosity, I went to ExpertFlyer today to see what other seats were available and I was surprised to see that my seat 7H was occupied but my daughter's seat in 7K showed as available. I looked up the seat availability on the JAL website and 7K showed up as available on their site as well. Fortunately I was able to immediately confirm my daughter's seat in 7K through JAL's "Manage My Booking", and her seat is now showing as occupied on both the JAL site and on ExpertFlyer.

I should know better to always follow up with the operating carrier on seat assignments. I do find it interesting that JAL showed my daughter's seat as available despite being a OWE companion; I just want to pass this data point along for other OWE flyers so they don't rely on AA (or other OneWorld airlines) for companion seat assignments when booking JAL award travel.