I saw a video saying NBC, Hollywood and the Jews were behind the Polish jokes in the 60's and 70's
The theory is that Jewish comedians playing at tourist hotels in upstate New York state began them, transferring the old East European Jewish idea of Slavs as dumb horndogs with Poles standing in for any Slav.
Another is that these were old pan-ethnic jokes that had passed to different nationalities over the years and stuck with Poles after the 1920s immigration slowdown.
In communist times police jokes in Poland were very much like Polish jokes (some of them were identical) - IIRC in the USSR there were police and Armenian jokes but that might be mixed up with Radio Yerevan jokes.