Just search for any Norddeich-Bremen connection in the affected three months on the DB route planner with "only local transport" ticked and you will see the label on every second train. Well, after clicking "Show more information" and carefully reading the grey on white text.

Edit: I tried in English and the warning didn't show up... Hopefully this link works as an example: https://reiseauskunft.bahn.de/bin/traininfo.exe/en/45678/209...