A lot of inexpensive beads were made from polystyrene, until acrylic took over as the main plastic material for beads - not sure exactly when. It is hard to find any new polystyrene beads - I've looked! On the other hand, I have a few sample cards from Czech R. with polystyrene beads from the 1960s - sorry none look like yours. Also, all of the "new old stock" plastic beads I picked up in Czech R. earlier this year were polystyrene beads. Polystyrene was a commercial product starting in the early 1930s and it seems a lot of bead and other article production switched over from Celluloid to polystyrene in the 30s and 40s. The injection molding technology is the same for both materials. I saw a display on this in the museum in Neugablonz. Very hard to know for sure whether your beads are pre- or post- WWII. Note: Neugablonz was founded after the war, but the museum has a lot of info about the history and industry of the people who left (well, forced out of) Gablonz to found Neugablonz.
Polystyrene beads used in ethnic compositions are frequently very pitted and scuffed-up since they are not very resistant to wear, as compared to acrylic, which is harder. This gives people the impression that they are "quite old". Or, since the gloss wears off quickly, I've seen people confuse polystyrene beads with old amber since old amber can have a similar non-glossy, pitted surface. Occasionally there are light yellow polystyrene beads being sold as "lemon amber" for example.