A good place to post your query would be the Erdman & Erdmann surname message boards. There are almost 500 combined Erdman Erdmann and even Ertdman & Erdtmann occurrences culled from local German newspapers and indexed in "Milwaukee's German Newspapers; an index of death notices and related items" (1844-1950). But I don't see any direct matches to the names/dates posted in this thread.
Gary Rebholz, originator/compiler/editor, Milwaukee Wis.firstname.lastname@example.org
Indexing Milwaukee's German newspapers continuously since 2007... helping family researchers find their ancestors among Milwaukee's 99%.