And I have learned the difference between a polska and a slängpolska...
Yes, there are literally dozens (and dozens more) distinct varieties of polska...of which slängpolska is a subset, not to mention the related forms found in Norway such as pols, springleik, springar and so on. It is an incredibly rich and fortunately well-preserved tapestry of musical forms going back centuries.
The late Jan Ling of the University in Göteborg (Gothenburg) has written a fascinating book titled "History of Folk Music in Europe" which should be a must-read for musicians and music lovers. Other interesting books on Swedish music are:
Einar Övergaards Folkmusiksamling compiled and edited by Märta Ramsten
K P Lefflers Folkmusiksamling
Svenskalåtar
The last is a 13 volume set of "official" tune settings from all over Sweden. However, the degree of "standardization" having been applied by the original editors has been regarded as somewhat of a homogenization of the music volumes such as Övergaard and Leffler which have been printed in the original form and hand of the collectors themselves resulting in a fascinating essential representation of the music.