@andreaswiedenhoff @diningcar I did a couple of Inter-Rail trips around Europe, 1993 and 1996, and this sort of thing wasn't uncommon - particularly on night routes, there would be crowds of people trying to get on to particular carriages, while others were ignored.
Swiss carriages were particularly prized, even on routes that went nowhere near Seitzerland, while everyone tried to avoid French sleepers - they are great if you sleep on your back, but if you sleep on your side... OW!
It wasn't uncommon to see a seemingly random collection of Belgian, Dutch, French, German, Czech, and Italian stock on any route.
I would imagine that, with the EU expansion, and Spain re-gauging it's network, that trains are even more eclectic and exotic these days.