I've seen on the DB Bahn and OBB websites that for some routes "It is mandatory to hold a valid ticket in local lines," e.g. from Garmisch-Partenkirchen to Innsbruck. I have a Eurail pass valid for both of these countries, but is a local ticket or something needed for these routes? Thanks!
The stretch between those two stations is a self control area - there won't necessarily be a conductor on the train. But you may well see a fares inspector or two.
So you must have a valid ticket for your whole journey.
If you have a Eurail pass valid in both countries and valid on the day of the journey, you have a valid ticket.
Thank you, Nigel!