Clear as mud.

From a foreigner's perspective, all I know is I brought a ICE ticket on bahn.de from "Frankfurt(M) Flughafen Fernbf" to "Düsseldorf Flughafen." One would have expected that would coverage transportation to the terminal. Who knew you had to buy an additional ticket for Skytrain or walk the 2.8 km between the train station and the terminal.

No idea if the ticket is "special" enough to be a a special DB tickets, such as City plus, NRW-, Schöne-Reise-, Schöne-Fahrt- and the Schöner-Tag ticket"