Some of the family have dropped the last "n" in the last name others have not. When my grandmother was married her "official" last name was Munstermann, with two N's.
Minnesota, Marriages from the Minnesota Official Marriage System, 1850-2019
Name Bertha E Munstermann
Marriage Date 15 Apr 1936
Marriage Place Swift, Minnesota, USA
Spouse William H Harste
Certificate Number K-310