You have a point, there is always the risk the messenger might decide he has had enough of Bangkok and go back upcountry with the passports still under the seat of his motocy.
Another risk is power struggles between factions within a certain Bureau or a new boss halting things to make it clear where the "appreciation" has to flow (Lars told me that happens with every change). You could be caught up in that with not enough time left. Recently at CW things were very difficult for agents - whether that was all agents or those not in a favoured subgroup was not clear.