Oh yes, Tahoma does show 'normal' and 'negreta' in FontBook on the Mac. Maybe this is a bug of the OS, and not FileMaker's fault. So I take it that Negreta means bold, or rather duck bold.
As for the new style of supplying variations, FM14 now provides other variations such as Thin, Light, Condensed, etc. Thanks for pointing that out. I consider this a new feature, which FileMaker didn't announce as one.
Alas, FM14 didn't actually remove all the 'faux' bolds and italics because Tahoma comes only with Normal and Bold but if you press the italic button, its 'faux'.
Also note that, FileMaker on Mac OS can use OTF and TTF fonts but MS-Windows use TTF fonts only, no OTF. If you use custom fonts for both platforms, pick TTFs. But then again, iOS will have to use another theme using its build-in fonts because you can't install fonts there.