It appears that tube station can be used even it's only "ghost". Note that it's used only for "arriving" dups, not departure.
Or maybe someone is going to tell me that dups can go out of the tube without the station, so even it should be weird, I would admit that it's not a bug and learn something, and my report could be closed
My save's joined. It's right on the Transit Tube Access in the screenshot.
Have a nice day !
Build a transit tube, build the station, and wait or force dups to use the station when it's not built yet.