Follow Up - When Things Don't Go Right

So, as it turns out - the postcards DID in fact get delivered - but was received at various addresses between 4-6 weeks AFTER the event.  Since different people received the postcards at different times, it would tell me that they got hung up with different carriers at separate post office locations.   This would make sense if the postcards were sent at bulk rates, but they were sent 1st Class Mail - absolutely no reason they should not have been delivered prior to the event.  Doesn't help the non-profit that was holding the event though :(