In many languages, dictionaries have existed for centuries but it wasn’t until 1604 that the first English dictionary, A Table Alphabeticall, was written by schoolteacher Robert Cawdrey. Only one copy exists, at the Bodleian Library in Oxford, England, so it probably wasn’t in widespread use. Other dictionaries followed, but it wasn’t until Samuel Johnson’s A Dictionary of the English Language (1755), that spelling became more standardized.
It’s no surprise that surnames also lacked standardization. I’ve seen documents where a surname was written one way in the beginning and changed somewhere in succeeding paragraphs, or the signature didn’t match the previous paragraphs. Sometimes clerks phonetically interpreted the sounds of a name. Sometimes handwriting or signatures were illegible or hard to read.
Sometimes surnames changed over time. For example, the How family who in 1707 built the Wayside Inn in Sudbury, Massachusetts, eventually added an E to their name, making it Howe. (Perhaps they didn’t want their surname confused with the word “how”?) Purportedly, author Nathaniel Hawthorne (1804-1864) added the W to his name to disassociate himself with his hanging judge ancestor, John Hathorne (1641-1717).
Sometimes names show up in various ways in early records. John Jepson (1610-1688) and his family are known in early Boston records as Jepson, Jephson, Jebson, Jipson, Gipson, and Gypson. However, in one published record he’s listed as John “Gibson” when he and his wife Emm were admitted as members to the First Church of Boston in 1670. It’s only one record, but that misspelling caused me to do many hours of research on what was really the Jepson line!
Always record the variable spelling in your notes. Keep a list of the different spellings you find to make it easier to check variations in indexes, databases, and documents.