For the fun of it, I just checked current incarceration numbers. It is about a 20000/per year. To be fair Czech population was lower back then (although I am not sure if they are not counting Slovakia as well, as they were one country) but still just, 200000 is pretty low for 40 years of “totality”.
Beets is great but it also uses musicbrainz so won’t really help OP.