You really have to forget about what the website says; it is irrelevant, it does not apply to your fare. You are holding a NRT-LAX L class coupon, and unless you want to have that ticket reissued, and pay the fee, and find alternative "L" class seats available, you are just going to have to accept that there is no availability other than the dates I gave you, or AA makes available to you if you plead your case.