It all depends. But if experience is any guide - my international Y -> J VIP upgrade success rate is perfect save for one isolated disappointment in 2002. That's better than 98%. Some were confirmed at booking and the others cleared prior to the day of departure. A couple cleared at the gate. Odds are your upgrade requests will clear. Mine always do, and others report the same experience. AA will certainly release more C if it thinks it can't sell them as D or J.