"nach Verfügbarkeit" indicates the problem. This bonus ticket has to be pre-booked for a specific train connection WELL in advance. They only allow a very limited number of those free bonus tickets per train. If there is no availability any more, bad luck.
Disclaimer: I have never used the international bonus, only within Germany where I had the problem indicated above. Can't tell about the Paris or Caen problem. Depends what the ticket counter can book.