Originally Posted by skimthetrees

SEA is tougher because there is only one flight a day. Other gateways like SFO and LAX have more.

You can use AA to search availability since AS has some end of schedule booking bugs you will need to use one of the workarounds to book the last few days of the schedule. https://www.flyertalk.com/forum/34973234-post77.html

SEA has 1J on 4/8 and 2J on 4/9 at this moment and that's it. No economy. If you want earlier than that you should book though another gateway like SFO if you see it available. The $12 partner booking fee is non refundable (except within the first 24 hours?) but there is no change fee (you will not be charged a second partner booking fee to change, only to cancel).

Edited to Add:
JL awards near the AS end of schedule are not released in batches. They have all been released prior by JAL, who releases awards 360 days out, and other programs that can book farther out take most of the good ones before AS gets access.

You can use other partners, such as BA, to look at the availability slightly beyond the AS booking window to see what may become available to AS once it enters their booking window.