Just upgrade from J to F (same flight same date) on my LAX-NRT segment (LAX-NRT-Asia). The issue is that we could NOT do it online using Change Reservation tool. AS website shows F availability on all date except my departure date. Called AS and ask for partner award desk. The agent told me she could not get the F seats to show up either and she would need to contact supervisor(?) to upgrade me. As I compulsively refreshed the reservation screen, I saw that they added the F seat to my reservation first then removed the J seat. New ticket issued and I was able to select F seat on JAL immediately. However, I don't see my award J seat go back to inventory and available to book.

I think a workaround for this is to upgrade to F to whatever date AS website allows and then change it back to the original departure date. However, I didn't have the courage to try that lol !