Mostly I've been asked that question by all of the Trammell descendants who have found the book. That would be the descendants who spell their name most often as Trammel or Trammell, but if you look in the old court records, it might appear as Trammill, Tramel, Tramil, or Trammael. Their Cornish ancestors might have also used Tramell, Tremayle, Tremmel, Tremmell, Tremmil, Trimlin, Trumnell, or Trimnill.
So I was happy to narrow it down to just two standard spellings.
But it wasn't me who did that. It was an outstanding historian AND Trammell descendant, Jack Jackson.
I explain the method to my madness in the book within footnote 3 in Chapter 3, page 228. (You are reading all the footnotes too, right?) Given both Jackson's stature as a historian and a descendant of Old Nick, I simply accepted his convention. Here is the explanation.
"On old maps, the name of the trail is most often seen as Trammel, two M’s and one L. The Handbook of Texas spells it as such. Jack Jackson, a noted historian and Trammell descendant, made a case for Nicholas Trammell’s name to be spelled with two M’s and two L’s, a change also reflected in the Handbook of Texas. This convention will be used throughout this work."
So there is the answer. Rather than choose one spelling, I chose two. But it was no labour at all.