>Presumably he didn't have an 11th fret, so his 11th fret is our 12th, >if you see what I mean. :-)
Yes, that makes sense, as do the other responses about the reasons that there might not have been an eleventh fret. Wouldn't that mean all or most of the lutes at the time all were set up this way? Neusidler would have used the symbol that would have been useful to the most player, even if his own lute was idiosyncratic. A little later, Molinaro (Fantasia XII, 1599) uses 'X' (ten), 'n' (eleven) and '13' (thirteen), but I cannot find a twelfth fret marking! Does anyone know what the 'n' stands for? To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html