Hi Ivo,
I think this is one of those problems caused by the Czech tradition of first male offspring carrying almost the same name as the father. Certainly there is a Miroslav Janku, working for ZBS in the 1960s/70s?? (sorry reference material is in France), and for Crystalex and Obalunion in the 1990s, but he was no Rudolf Schroetter......
Regards,
Marcus