Robert, I now believe that the variant spelling may have happened not long after the adoption of the surname. Surnames being a bit over a thousand years in use. (for more effective taxing)Matter of fact, the double TT has an A sound when spoken in French so that a Norman scribe may have been the source of the very first variant spelling. It could have been in either Lancashire or Yorkshire, England around 1100. I feel certain it is a very valuable clue as to the origins in that time period. I would definately gues that the Whitsitt/Whitsett surname first appeared south of Hadrian's Wall and was the outcome of Norman administration after 1066.