Not giving a solution, but just adding some information.
During the past years, depending on the version of AutoCAD and on the different configurations, not only in my company, I have noticed that programs like CorelDraw or similar ADD/Overwrite TTF fonts that become available in AutoCAD.
Last but not less important, I know a big company here in Italy that has different software configurations and have experienced problems with the TTF opening the same drawing with AutoCAD 2005 and with AutoCAD Map 3D 2008; the strange thing was that both computers had the same font, don't remember it at the moment, but in ACAD2005 it was listed with a different font name that the one displayed in MAP2008, although the TTF file was the same.