Ticketing in the VRR is a bloody mess!
I don’t know as I like to know the answer too, equally what’s the best ticket to buy for local transport within the Dortmund city limits?
For trip inside one town it's always Preisstufe A (even if the town consits of two zones...), specificly A3 as the service level is said to be good enough for that (but Duisburg was also in the discussion for getting A3 status, so that does not say anything at all). There are single, "4-er Tickets"(for 4 journies) and various versions of n*24hrs tickets (with n in {1,2} i.e. there are 24 hours and 48 hours versions).
I thought I understood the VRR zone system and that a B ticket simply allowed travel to the adjacent zone.
https://www.vrr.de/en/tickets-fares/tariff-zones-regions-fare-categories/
However I have now learnt that a B ticketholder can allow travel to 2 zones away eg. from Muelheim an der Ruhr, as far as Bochum or Duesseldorf.
So if you start in Bochum and want to go to Duesseldorf and back, you'd need a D day ticket if bought as paper ticket.
Could you instead buy a B day ticket on the app specifying a notional starting point of Muelheim an der Ruhr?
Looking at "the beast" (
https://www.vrr.de/fileadmin/user_u...tarifinformationen/Preisstufenmatrix_2020.pdf) for single use tickets, Mühleim a/d Ruhr indeed has the nice property of being a "B" journey to both Bochum and Düsseldorf Mitte/Nord (but not Düsseldorf Süd). Your loophole would thus be perfectly possible on a day ticket (but not on a single!) starting at Mülheim a/d Ruhr, becaus you could have come from Mülheim first thing in the morning, went to Bochum and can then also go to Düsseldorf. The VRR system is very intensely filled with such things and poorly trained RPI, but your trick is perfectly valid!
The system might be designed in a way to discourage public transport usage, which is quite a pleasure as most cities in the Ruhr area are rather poor but rather pay for some idiotic prestige projects (various projects (not only) in Duisburg spring to mind) rather than investing into the provision of decent transport. I moved to Garching (near Munich) last year, were the bus service is much better, (20 minute intervals on a Sunday for a weeny "city" (it's only got that title through a joke on a TV debate) vs. 30-60 minute intervals in Duisburg).
Another oddity is that two A singles are cheaper than a B single and if you are prepared to levae the vehicle at the overlap between the two (there are some weird overlap rules, e.g. some areas of Düssledorf Nord to some areas of Duisburg Süd are A3), you can travel cheaper, but if someone finds out, you could be penalty fared.
It just an awful system, completed by them making up their own rules about products they don't have control over (according to the VRR, a "Schwerbehindertenausweis" (in some circumstances, disabled people get free public transport in whole Germany) is only valid to the last German station, whilst it's actually valid (as supported by national law) to the tariff border point - but the revenue training the staff get seems to be very much VRR based - not knowing what Emmerich(GR) is on a service passing there, does not really show any understanding of ticketing on international services).
But once again: Using a digital B 24 hours ticket in the way you suggest is fine and in my eyes not questionable.
