The Martin 000-18MC Martin Carthy special edition guitar has a zero fret, as has the 000-18 that he has played since forever. As can be seen from the picture posted by his son, here, so had Paul McNeill's Martin which was, if I recall aright, a 00-18.

Personally, I've never been totally convinced by the alleged virtues of the zero fret, despite its use by Fylde and a number of other respectable makers, but I cannot recall ever seeing another Martin with this feature, nor can I find any reference in the standard Martin reference books to the zero fret being available as an option.

As it affects the scale length, I would have thought that it would have to be incorporated from new, but I could be wrong here.

Does anyone else have any knowledge or opinions on this admittedly rather arcane subject?

Alan