Assume you are starting in Berlin and ending a train trip in Prague. You have an Eastern Europe pass but it only covers from the border to Prague. How does this all work when you are starting in an area not covered by the pass like Berlin. What if you were on a sleeper train say starting in Berlin and heading to where your pass picks up in the Czech Republic or even to Krakow.
There is no Berlin-Praha night train. It's too short a route. You could buy a ticket in Berlin to cover the part of your route from Berlin to the border and let your pass cover you from the border to Praha. However, if you book well in advance (up to 90 days allowed) at www.bahn.de, you can get a Europa-Spezial fare of 29€ for Berlin-Praha and you would save yourself a pass day for use later.
There is a Berlin-Krakow night train. In that case you should buy a ticket in Berlin that will cover you as far as the border and will include your sleeping accommodations all the way to Krakow.