Unfortunately, I cannot answer your question to your satisfaction.I am a decendent of an Abner Neathery who came to Texas between 1836 and 1837.I have found information on the web that suggests his father was Samuel Neathery, whose father was Robert Neathery, Sr., whose father was Thomas Neathery, Sr.
Documents in Texas spell his name each of the ways you have suggested including putting in the "L".
I just found out that Abner Neathery is my GGGgrandfather within the last week.I have only been working on genealogy of my family since December 1999, but I find it fascinating.
Do you have any history on Thomas Neathery, Sr.decendent tree?Abner states in the census that he was born in North Carolina.
I guess when one family gets mad at another, they change the spelling of their name -- that is if they knew how to spell it to begin with.