I see the XI as meaning "a note above X" It would have been immediately obvious to the player what note was called for. If that's the case, these aren't typos but shorthand; ealy notation always has an element of shorthand.
Also, the tab does not refer to a half-step; the half step ideogram is a "placeholder" for the note. Otherwise, you would not have ficta, a situation that would have would have been absolutely impossible for a trained renaissance musician. dt To get on or off this list see list information at http://www.cs.dartmouth.edu/~wbc/lute-admin/index.html
