I'm not so sure either. I have noticed that a few plants reported around Bluets Block and Sutton look suspiciously like D. nigromontana. I should probably find the paper that describes each species and any that describe how they differ. As for this plant, I don't really know. Based on flowering time, this should theoretically be D. semilunulata.
ALA doesn't have any records from this area which is perhaps telling. Having come back to this sighting i'm thinking that the flower facing towards us has part of the lateral lobe folded back which makes it appear slim and pointed rather than rounded. Looking at the back of the other flowers the lateral lobes appear to be rounded which I think its a feature of D.semilunulata. The labellum seems very narrow though.
I would think the dark stem, the high dorsal sepal with the lateral sepals and petals folded back would all suggest D. semilunulata but the midlobe is folded more like D. pardina. These are not easy and variations seem to outnumber the one truer to type. I understand the D. semilunulata type specimen collected in 1942 was from Mt Jerrabomberra.