My Grandmothers family was Johnson and I am finding as I research that it may have been Johnston back in the 1700s and was changed as was a lot of names for various reasons when they came to America. That spelling has shown up in our history. I do not recognize the name you mentioned in our background tho. When pilgrims landed some changed their names and some I found changed due to native dialect. It seems another side added an S somewhere along the line and I suspect it came about due to the dialect of the area. ex: you and your family for youns, ...etc. Hope this helps.