Poland under communist rule was till 1989.
All coins were eagle dont wear crown in obverse are PRL time.
3rd republic coins are all coins where eagle have crown on his head.
Of course there was also transitional period from one currency to another. https://en.wikipedia.org/wiki/Polish_z%C5%82oty where eagle wear the crown but because of hyperinflation they are also considered as PRL time.
The reason while coins from PRL period you can find in3rd republic is simple. When they were add to the catalog there were no such option like ruling authority. It was a bug as they have been incorrectly assigned by robot ? PRL and 3rd republic both have the date 1989
Regards,
Damian
Former numista referee for Poland and half of african countries.
I invite you to my FB group about commemorative coins :
https://www.facebook.com/groups/1635288620035921