All I know about Isaac Martin is what I read in Phifer's book about his being indicted for being a Loyalist and that Phifer found him on the 1790 Census in Burke. I did not check the census myself.
Since you have done extensive research on the Whites in Burke Co., I guess even Phifer could be wrong as computers, DNA, etc., were not advanced in his day. Just thought I'd include that in case no one had further research on the Whites.
My Ambrose Williams entered three separate pieces of land in Burke Co. in 1778. His daughter Elizabeth married James Kerley and also lived there prior to moving to TN. Ambrose' wife died during the Rev. War and he married Jane Hiatt Inman who married first to Hezekiah Inman Sr. The Inmans also lived in Burke Co. I have them pretty well documented but I'm searching for Ambrose' second marriage to Jane Inman - have't found that yet.
Ambrose' first wife, Mary Moore probably had Moores who lived in Burke but that research has come to a brick wall there.
I have a problem in Burke as most of the land for the Kerleys/Inmans is under or on the shores of the James Lake. It has been difficult research. I'm searching for the burial of Mary Moore Williams - no luck on that yet.