FYI:
BA and AS are agreeing that YVR-NRT on January 18 has 5J availability (YVR-NRT usually has good JL J availability, so does SAN-NRT), which seems to preclude the possibility of some sort of blanket block on AS J redemptions on JL.
So maybe clarify what you're seeing? Are you searching at edge of schedule or something, on routes where things usually come open immediately? Out of LAX/SFO/JFK maybe?