I thought I would copy this thread from the CO2 Dev Forum just to keep you abreast of development work we are doing. This is just one of the issues we have been working our way through recently. I'm aiming to release a new dev build 5.1.30 by the end of the week. If the testers come back with the all clear then we'll aim to get out a release version for you all to update your game engine and modules.
This is a test scenario that Daz sent me last year to illustrate how a unit will get supplied even if the single forest road between it and the supplying base is completely interdicted by enemy units.
I ran the game for 3 days and every supply column got through.