I just saw a similar scenario yesterday in Zwerg Tube’s video series, which is in German. I believe it’s number 22 or 23? He connects a second oil source via road vehicles to a rail station which was already carrying oil from a different oil source to a refinery. The newly connected source was not delivering oil anywhere (presumably it was too far away to even deliver anything on foot) and eventually was running full production. Now, oil was being carried from the source to the rail station and waiting at the station to be carried by train to the refinery. So two things happened: by connecting the refinery with a bus freight line to the freight train station, the delivery time of the oil was reduced enough to make production start up again. This required the software to recognize that a transfer of goods at a station as part of the path as necessary. I don’t see why this same process wouldn’t occur for an all rail network.
Hope that helps!