Thanks for this.

I took a group of Scottish grad students on the Ost-West Express (Oostende - Warsaw) in the 1970s and remember the trip very well. The carriages were mounted in reverse order - Soviet ones at the front, then Polish, East German and West German, with the dining car at the end; it was removed (and a new one added) as you departed the country where they'd dropped the carriages.

We had several changes of traction - Belgian to Aachen, DB electric to Helmstedt, DDR to Frankfurt-am-Oder where the Polish locos were added. I assume they switched to Russian units later but we got off in Warsaw.

Transiting Berlin was really interesting and quite depressing. The wall and no-man's land from the train: