Sounds to me like the person doing the labeling isn't sure where the specimen is from. Werfen is a town near Salzburg, and I believe Imlau is a town too, but I don't know what Pongau is, possibly another town.
I think your searched locality is Höllgraben, Pfarrwerfen, Werfen, Salzburg, Austria Pfarrwerfen is 2 km south of Werfen and Imlau is about 1,5 km west of Pfarrwerfen. For the Höllgraben locality you found the following hint: "A small southwestern branch of the Salzach valley, located just west of Pfarrwerfen." So Höllgraben and Imlau designates the same place.