convoy question

[Laffertytig]

how do convoy routes work in SH4? i read somewhere that in SH3 traffic for the whole is loaded when the patrol starts but in SH4 only 3 momths is loaded, not sure i understand what that means though.

for example, if a port becomes japanese during a patrol, do ships start to sail from it or is it only when you officially end the patol and start a new one that ports start to populate?

im not running TMO mod.