Most of the time. Sometimes the events come back around a couple of times (FF13, Yokai Watch, etc), otherwise I'd expect to see the rewards on the mogstation a year or so later. AFAIK the only year+ old crossover items that are completely unobtainable right now are the DQ10, some of the FFXI ones, and Yokai Watch ones (Yokai Watch probably has licensing issues preventing mogstation sales.)