In the United States, the spelling of words and names didn't settle down until the late 1800's when literacy became widespread.  Nor was the precise spelling of words even considered important until the 20th century, as long as the meaning was conveyed.  For example, our word "ton," meaning 2000 lbs, could be spelled ton, tonn, or tonne.  All three spellings would have been considered entirely acceptable to someone in the 17th, 18th, or even 19th century because they all represented the same sound.  Their attitude would have been that the purpose of writing is to communicate, and if your writing communicates your meaning, that's all that's required.  Anyone who has transcribed more than a few historic documents can tell you it is not unusual to find someone spelling the same word or name in more than one way — in a single document!

Words were sounds thousands of years before they were written down.  Human language is speech.  Writing is a feeble attempt to represent speech visually.  So, do not get "hung up" on spelling, particularly on the spelling of names.

Most of our ancestors were illiterate subsistence farmers.  Their names may never have been written down in their lives, except possibly in the church register when they were christened and later married — and on a stone in the churchyard when they died.  In our society, with general literacy and vast, cradle-to-the-grave record keeping, it can be very difficult to imagine what it's like to live in a society where few could read and few records were kept.

How many times in your life have you had to give your name and date of birth?  Can you imagine never having had to do so?  Can you imagine forgetting your birth date?  But people did forget, and they forgot because they went a lifetime without it mattering:  no forms to fill out, no classes to register for, no tests to pass, no jobs to apply for, no driver's license to get, no income taxes to file, no insurance claims — no credit to apply for.  What mattered was raising crops or making goods and maintaining a home and caring for ten or twelve  children.  Even a man as intelligent and literate and important as Jefferson Davis, President of the Confederate States, lost track of his birth year (he was uncertain whether it was 1807 or 1808).

To an illiterate person, their name has no spelling, only a sound.  When they said their name to a county clerk or census taker, how it got written down depended entirely on the knowledge and diligence of someone who may have been barely literate themselves.  And if the clerk was English and the subject German (or some other non-English nationality), the name often got slaughtered.

I can think of cases where, in one census year, all the persons of a particular surname in a county had their name spelled one way, then in the next census, spelled another way, then in the next census, back the first way.  These people were not changing the spelling of their name; there was a different person enumerating the census each time.  The same thing can happen when moving from county to county.  In one county, the clerk spells their name one way, in the next county, a different clerk spells it differently.  Let me repeat for emphasis:  by and large, the way you see your ancestors' names spelled in the records is not how they spelled it (or would have spelled it had they known how to read and write), it's how the person who wrote it down arbitrarily decided to spell it.

These arbitrary spellings — which prevailed until literacy became widespread — are primarily what we would call "phonetic" misspellings.  Clarck for Clark, Canady for Kennedy, Garrod for Garrett, Robards for Roberts, Witmer for Whitmore, Thaxton for Thackstone, and so on.  The greatest misspellings were of non-English names.  Many of these names were converted by English-speaking clerks to equivalent, or at least similar-sounding, English names:  Braün became Brown; Müller became Miller; Ihle became Ely.  In the case of given names, English spellings were substituted for German ones:  Sanna and Susanna became Susannah, Catharina became Catharine or Catherine or Katherine or Kathryn, Maria became Mary, Andreas became Andrew, etc.  Other names simply acquired an Anglicized spelling:  Dreischmeyer became Dreshmire, Dannemann became Denman, Schantzenbach became Johnsonbaugh, Schaeffer became Shafer, and so on.

With experience, you will learn to not attach so much importance to spelling and to "roll with it" when you find a novel spelling because the important thing is to recognize the name regardless of how it is spelled — and to always try at least the common variations when searching via computer.

One of the best examples I've found of how German surname STRAUB — my mother's maiden name — became converted to it's most common variant, STROUP, is in the marriage bond of Jacob STRAUB/STROUP & Betsy DILLINGER.  Note how the clerk recorded the bond as "Jacob Stroup," but Jacob signed the bond, in German script, as "Jacob Straüb"!