What I have found is the biggest stumbling block aren't the "Soundex" kind of spelling variations that are phonetic - but where the record keeper has misheard the name, or misinterpreted what they heard because of accents - or their handwriting was the pits and the name has been indexed or transcribed as something off the wall - i.e. Laslo becomes Taris. Illiteracy in prior generations was not uncommon and that means the person giving the information is completely at the mercy of the registrar or census taker. One arm of my family in Scotland were illiterate until the the later 19th century so we have members of a single household from the 1830's who ended up with a wide variation in surnames - which subsequently "stuck" - leading to lively arguments among descendents about whose spelling is the "right" one i.e. Brebner, Brember, Brymner, Bremner etc. M.