Spelling of Surnames and Given Names
There has never been a time when names have had a standardized spelling. In early church records it was up to a priest how the names were spelled and different priests within the same parish had different ideas on how names should be spelled. When a census taker recorded a person's name the census taker decided the name was spelled. You may need to be creative when trying to identity how a family names was spelled by a specific census taker. See Name Variations in United States Indexes and Records.
The soundex system was invented to help researchers check many variations of surnames at the same time. If the soundex option is not available for the records you are searching, try to spell the name in as many ways as possible. For example Reed, Reid, Ried, Read, Reedt and search under each spelling. First names were also spelled in many different ways and nicknames were frequently used such as Sally for Sarah and Patsy for Martha.