I searched for their death dates in FamilySearch but didn't find them.
The St. Cloud times Index, https://griver.org/sctimes-index/
didn't have an obit for Mathias.
They had one for an Agnes Bieniek, May 2, 1974, p. 14 , husband=Joseph.
I have a feeling that the death dates are incorrect. You can contact the Stearns History Museum & Research Center, http://stearns-museum.org/
and look for their full death dates. After you find them, you can look for thier obits at Minnesota Digital Newspaper Hub at no charge. Successful Searching!