Of the 3,661 surnames there are a total of 20,051 spelling variations. When considering just how your ancestor's name might be spelled, think of the individual letters, and how they might sound when spoken with an Irish brogue, or a southern drawl or a heavy Germanic accent. Complicate matters in your thinking by imagining the stress at a local port during the 19th century, teeming with newly arrived foreigners. Its your job to write down each of their names in the customs passenger list.
Babies are crying, people are tired and perhaps sick.
You just want to get through this line of folks. Try as you might, its nearly impossible to understand the accent. Hardly anyone except you and your co-workers. Frankly you are afraid you might catch something contagious from these people. Now you are beginning to get a clearer picture of how the spelling of a name might be changed.