My Grandmother Hannah Cowie was a Smith before she married.
The furthest back I've gone on the Smith side is my 4th Great Grandfather Alexander Smith and his marriage to Jean Reid record in 1788. (second Smith on the page.)
The family was recorded in Rathven, Banffshire and many of them are still in the area.
I've not come across many misspellings for Smith, Smithe, Smyth, Smythe, Snith