From a distributor point of view its very straight forward... this one paid first.. heres your 50 or so machines. Then you paid up so heres your 75 machines etc etc.
Overseas sales sitting in containers at the docks will be considered as contract fulfilled. They may take a month to get to the destination and meantime a US distributor with less travel may well take reciept of his games beforehand. But as far as machines out the door on first pay first play basis i see it as a very simple excercise