Thanks, my OWE is indeed already entered. I spoke to a JAL staff on the phone, who said indeed my membership was there and I have access to the full inventory, but the flights were simply very full and all the window seats were actually allocated. But not being a regular with JAL, I wasn't sure if that was the whole truth. At least on CX, my main airline (I'm based in HK), they'll make up stories about the bassinet and whatnot in F attempting to hold back a few preferred seats, but actually anyone can snag them.

I see, I am on a cash J fare but it's one of the discounted sub fareclasses, definitely not fare J. Either "X" or "D" I believe. Does that make a difference? FWIW, the terms are great - no fees for reservation changes, rerouting, refunds, etc! They're remarkably flexible, without having to pay full J. At least as someone used to CX, the flexibility is eye-opening.