No, have to contradict this. My very 1st trip to the then CzechoSlovakia in communist times-with visa and all that, was via the very MAIN border point at the time, and about only rail-border to from BRD, and that was CHEB. Overnight train Frankfurt-Praha, the old style 6-seater compartmt with brown plastic seats so much used by DB (still Bundesbahn in those days). Cannot remember how exactly it was done, but took quite a while and only after that the train suddenly and to my surprise became quite full with locals, well used to that all.
Currently sit in the Metropolitan EC-train from Budapest, for me now till Bratislava, having had the MAV and ZSR conductors pass by and stopping at the 2 border posts Szob then Sturovo, the stretch we now pass is under reco for 2nd track. Will pass 2 more later created border posts-Kuty/Breclav etc. as Brno is final destination for today. Still on an Interrail, so not using my free senior Slovak railpass and in HU only he BKV free senior travel. Now passing a blue plastic ´laminatki´ goods train from Cargo Slovakia waiting for the track to clear.