Surnamedb is quite a useful site for looking at incidence and frequency of the name. From looking at surnamedb.com I would say the S*NN*T registered surname study (Guild of One-Name Studies) has considerably more information and detail than surnamedb.com as I focus on family tree reconstruction and adding detail about individuals from a very wide range of sources, not just the incidence statistics of surnamedb. Surnamedb also repeats information about the origins of the name (widely published online) that isn't entirely correct or complete, and again, I have a lot better sourced and verified information available. I also have quite wide networks of other researchers of this group of names, and am able to put people from the same ancestral groups in touch with each other.
Yes, all those variant spellings you note are ones I have come across and include - and a whole lot more. Just about every combination of vowels, and either one N or two, and one T or two can occur - often wrongly recorded initially, but then becoming the spelling for a particular branch of the family.
