I had to edit the lisp to point to where the fonts could be found on my system, some were at "C:\\Users\\Dan\\AppData\\Local\\Microsoft\\Windows\\Fonts\\"
Also windows renamed my font to have a hyphen, while your lisp did not: "Helvetica-Bold.ttf"
After that, using c:fontsub - it seemed to work, attached are screen shots of the styles before and after. c:fontremap worked also, only changed one other style so I didn't save an image.
sorry - no ideas. I would work through the code of a trouble font substitution and see what happens to look for the bug.
also, had to use DWG TrueView to convert down to v2013 so I could open. No idea if that changed anything.