Do you have the birth certificate for Fred Henry? Is that how you know he was born in Detroit or are you going by a death record?
What about his siblings? Have you traced them?
Since the 1920 census shows that Anna was born in Michigan, have looked for Carl & Anna's marriage record? They sure seem to have missed the census taker for 1900, 1910 and 1930. Or their name was really messed up.
Have you tried to trace Anna?
Was Carl Lutheran or Catholic? Have you tried finding a church record.
What about obituaries? I thought I saw a 1961 death for Carl in Petoskey on Ancestry.com
If Carl worked under social security, send for his application. Think it costs about $27.00 now unless they raised it again.