@jon I feel a bit rude asking, but do you think it's against the rules to combine two of these pass journées to travel in three departments on a single train ? I know you got told off once for splitting tickets. I'm wondering if the rules might be different for "all you can eat" tickets.
Marseille <-> Nice in a day for two adults is 4*~€40=€160 with four singles or €35+5+20+5=€65 with an 06-83 and a 13 pass journée, so it's a big potential saving.