Hmm, so when you see a person, who by ID resides in Munich and wears a Bayern jersey, you can tell that this person is in fact 1860 or Augsburg fan ? I couldn't and I doubt police officers could do.
There were matches in the past, where away fans weren't allowed. This was checked by postal code on the ID. If Bayern was to play in Bochum and no Bayern fans were allowed, then of course a Bayern fan living in Bochum could enter the stadium - but not in the away block and not with Bayern merch. A Bochum fan living in Munich and travelling to that game, could enter, but only as season ticket holder of Bochum.