In my experience, phonetics has had, and continues to have, a tremendous impact on the spelling of any word or name.Think about it.
A newly arrived German immigrant would pronounce his name with a German accent.A person writing down his name, perhaps a person of a different ethnic background, would almost certainly write it differently than Mr. Kettenring would have, had he been the one doing the writing.When a document was written, or census information taken, the person doing the writing was responsible for the spelling of a name.And he/she most certainly spelled it the way it SOUNDED to him.It would appear that no one asked anyone, "how do you spell your name?"
Twenty years after Mr. Kettenring's arrival in America, his pronunciation of his surname might have changed as he learned to speak more English, and as he migrated further south and/or west his way of speaking English would have taken on a more localized accent.(It would appear that earlier immigrants were eager to learn the language of their new country.)
Thus, the original Kettenring evolved to Kettering, Ketring, Ketron, Katron, Catron, Cattron, Cateron, Catrine, etc.Have any of you ever seen the surname spelled as "Cathrine?"That has happened.My grandfather and a lot of folks "out in the country" pronounced their surname as "Ket-urn" but it was spelled Catron.To this day, in his home county, it is still pronounced with the first syllable sounding like CAT instead of rhyming with matron or patron, as pronounced by some of us who live elsewhere.
Other than the impact of phonetic spelling based on the pronunciation of a name, how do we explain the spelling of EUN for Ian; Julian for Julie Ann; Jones for Jonas; Cathern for Catherine, etc, etc.And what is the correct spelling for the surname Han/Hann/Hand?!!I found it spelled all three ways in ONE deed!