It is not always easy to decide between gnas and gnad, especially when both seem to be equally sensible or equally nonsensical. The typical examples would be dka’ gnas (or dka’ ba’i gnas) and dka’ gnad (or dka’ ba’i gnad). And what about gnas ’bebs and gnad ’bebs? See http://rywiki.tsadra.org/index.php/gnas_'bebs_pa (s.v. gnas ’bebs pa), where two kinds of meaning are given, namely, (a) “to settle down in” and (2) (ad sensum) “to bring down someone (i.e. in rank/status, etc.). One also encounters the spelling gnad ’bebs. Is it simply a matter of scribal ignorance or confusion? Or are the two spellings options (gdams ngag)? (By the way, note the use of the word gdams ngag here.) If not what is the historical-etymological relationship, if there is one at all, between gnas and gnad? I, for one and now, propose that gnas is “a point in space” and hence a “locus” and by extension it can mean something “status.” On the other hand, gnad is a very special or specific point of gnas. It is a “crucial,” “pivotal,” “critical,” “key,” or “decisive” point or crux of space, time, matter, topic, and so on. One (e.g. Mi-pham) thus speaks of an “executioner/butcher skilled in the gnad of life-faculty” (gshan pa srog gi gnad la mkhas pa) and “wood-cutter skilled in the gnad of trees” (shing mkhan shing gi gnad la mkhas pa). So apparently the “word-coiner” (gdod ma’i mgon po) was able to make this subtle (and to many confusing) semantic distinction by means of gnas and gnad. This is, however, my mere speculation.