I unfortunately missed this thread, despite previously having posted in it.

At DUS, I'd have been far more concerned about checked bags making such a connection to ZRH than about overhead bin space -- even as, or especially because, the bags would not need to be claimed until ZRH.

Unfortunately, once the irregular baggage handling report is filed at the destination airport, even something like an airline or IATA worldtracer system ends up being barely useful for passengers; and even the airline reps are largely powerless until the bags are found and entered into the system with an update from baggage handlers/ground handling agents at the airport where the bag is. At DUS, ground staff for the airline has been anything but generally impressive when it comes to these kind of matters -- but that's just my experience flying via DUS a fair amount this year and last. If the airline has a delivery contractor who drives the bags from the airport where you have asked to have your bags delivered, then calling them has sometimes worked out for me. Unfortunately, most of those numbers are country/region specific and it's usually the baggage claim agent at the re-tagged destination airport who is often reasonably well positioned to get that number.