This discussion on the Supply System is very interesting, but alas not much help to those trying to play the Game!
If this is true and there is no plan to update the supply engine, then alas the Game will never be really playable!
That is what I have read at the forum, mostly from posts about being wad.
I totally agree that the throughput of supplies should be dependent on infrastructure but to have units out of supplies when there’s an 100% infrastructure trail back to your Home Country is ridiculous.
One other small thing regarding supplies, ‘who?’ thought of the idea to have units going out of supply when transiting a Country that gives ‘transit rights’, or is this just another bug? After entering the first province the Units just sit there forever! You can’t even supply them by air, classic!
If it is true that units with transit access are not supplied, I can think of a reason for it.
If you are in an allied prov or home prov, its easy total all units and supply them from prov or path to supplies. But in the case you mention, I would guess the prov needs to be in two supply ques, one for owning country, and one for visiting unit. Basically the prov has to be supplied twice. If there are two units from different countries in a province, and they are not in a faction(able to supply from each other) then prov needs to be processed twice, once to path for home country, once for visiting country.
I would guess the system can not figure how to path through a province for two non allied countries. Seems to almost need to create a transit only data object that is alot like the prov object but only used for pathing supply of a guest country in 'transit rights' situation.
I would guess each prov holds info for supply and pathing, so if two countries have to path through a prov, which set of data is set the visitor or the owner? That would be my guess why that anomoly exist. And if done twice then the data stored for first pass would not still be there next day. But that is just a guess.
In the 'for fun' thing I am working on I ran into same issue.