I remember in 2008, Ayu was never mentioned to appear at a-nation, so I planned my Japan trip to arrive on the 1st of Sept. About 2 weeks, maybe even 1 week before the actual date (29-08) it was announced that Ayu would actually be appearing after all, but I couldn't change my flight plans that close to departure so I missed out on seeing her. Biggest regret of my life.
So don't count her out yet, she usually announces her participation very close to the performance dates at the latest.